Remote Sensing of Environment最新文献_第3页

Mitigating the directional retrieval error of solar-induced chlorophyll fluorescence in the red band 减小红波段太阳诱导叶绿素荧光的定向检索误差

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-11 DOI: 10.1016/j.rse.2024.114496

Zhaoying Zhang , Yongguang Zhang

Solar-induced chlorophyll fluorescence (SIF) is a promising tool to estimate gross primary production (GPP), but the retrieval of SIF is commonly noisy and highly sensitive to various interference factors. Particularly, the retrieval of SIF in the red band (RSIF) is more challenging than in the far-red SIF (FRSIF) due to the weaker fluorescence signal and the weaker absorption depth of oxygen at the red band compared with the far-red band. A comprehensive evaluation of all factors will allow a reproducible interpretation of SIF signals and advance the estimation of GPP from SIF. Recent studies have assessed the sensitivity of SIF retrieval to sensor characteristics, retrieval methods, and hardware specifications. However, none of these studies have systematically investigated the directional retrieval error of SIF resulting from the mismatch between irradiance measured above the canopy and the true irradiance reaching the canopy components viewed by a sensor. This study illustrated the effect of mismatched irradiance on the retrieval of RSIF using the commonly used standard 3FLD method based on SCOPE model simulations. The retrieval accuracy was highest in the hotspot direction, but it decreased as the observation direction was away from the hotspot. The relative root mean square error (RRMSE) was generally higher than 20 % in the forward directions. To reduce the retrieval error due to the mismatch effect, we proposed a modified 3FLD method (MFLD) by calculating the true irradiance reaching the canopy in a given direction based on geometric optical theory. The results showed that MFLD clearly improved the retrieval accuracy for RSIF, especially in the forward directions where RRMSE decreased by 10 % in most cases. For example, the RRMSE was reduced from 19.26 % to 5.50 % after mitigating the mismatch between the measured and actual solar irradiance, when the solar zenith angle was 40° and viewing zenith angle was 30° in the forward solar principal plane. Even at the nadir observation, the RRMSE was also reduced from 12.84 % to 5.64 %. In summary, MFLD can effectively mitigate the irradiance mismatch effect on the retrieval of RSIF. These results will improve our interpretation of the relationship between GPP and RSIF at different observation directions.

太阳诱导叶绿素荧光（SIF）是估算总初级生产量（GPP）的一个很有前途的工具，但 SIF 的检索通常噪声很大，而且对各种干扰因素非常敏感。特别是红光波段（RSIF）的 SIF 提取比远红光波段（FRSIF）更具挑战性，因为红光波段的荧光信号比远红光波段弱，氧气的吸收深度也比远红光波段弱。对所有因素进行综合评估将有助于对 SIF 信号进行可重现的解释，并推进根据 SIF 估算 GPP 的工作。最近的研究评估了 SIF 检索对传感器特性、检索方法和硬件规格的敏感性。然而，这些研究都没有系统地调查冠层上方测得的辐照度与传感器观测到的到达冠层成分的真实辐照度之间的不匹配所导致的 SIF 方向性检索误差。这项研究说明了辐照度不匹配对基于 SCOPE 模型模拟的常用标准 3FLD 方法检索 RSIF 的影响。热点方向的检索精度最高，但随着观测方向远离热点，精度有所下降。前进方向的相对均方根误差（RRMSE）普遍高于 20%。为了减少由于错配效应造成的检索误差，我们提出了一种改进的 3FLD 方法（MFLD），即根据几何光学理论计算在给定方向上到达冠层的真实辐照度。结果表明，MFLD 明显提高了 RSIF 的检索精度，尤其是在前向，RRMSE 在大多数情况下降低了 10%。例如，在正向太阳主平面上，当太阳天顶角为 40°、观测天顶角为 30°时，缓解了测量太阳辐照度与实际太阳辐照度之间的不匹配，RRMSE 从 19.26% 降至 5.50%。即使在天底观测，RRMSE 也从 12.84 % 降至 5.64 %。总之，MFLD 可以有效缓解辐照度不匹配对 RSIF 提取的影响。这些结果将改进我们对不同观测方向上 GPP 与 RSIF 之间关系的解释。

{"title":"Mitigating the directional retrieval error of solar-induced chlorophyll fluorescence in the red band","authors":"Zhaoying Zhang , Yongguang Zhang","doi":"10.1016/j.rse.2024.114496","DOIUrl":"10.1016/j.rse.2024.114496","url":null,"abstract":"<div><div>Solar-induced chlorophyll fluorescence (SIF) is a promising tool to estimate gross primary production (GPP), but the retrieval of SIF is commonly noisy and highly sensitive to various interference factors. Particularly, the retrieval of SIF in the red band (RSIF) is more challenging than in the far-red SIF (FRSIF) due to the weaker fluorescence signal and the weaker absorption depth of oxygen at the red band compared with the far-red band. A comprehensive evaluation of all factors will allow a reproducible interpretation of SIF signals and advance the estimation of GPP from SIF. Recent studies have assessed the sensitivity of SIF retrieval to sensor characteristics, retrieval methods, and hardware specifications. However, none of these studies have systematically investigated the directional retrieval error of SIF resulting from the mismatch between irradiance measured above the canopy and the true irradiance reaching the canopy components viewed by a sensor. This study illustrated the effect of mismatched irradiance on the retrieval of RSIF using the commonly used standard 3FLD method based on SCOPE model simulations. The retrieval accuracy was highest in the hotspot direction, but it decreased as the observation direction was away from the hotspot. The relative root mean square error (RRMSE) was generally higher than 20 % in the forward directions. To reduce the retrieval error due to the mismatch effect, we proposed a modified 3FLD method (MFLD) by calculating the true irradiance reaching the canopy in a given direction based on geometric optical theory. The results showed that MFLD clearly improved the retrieval accuracy for RSIF, especially in the forward directions where RRMSE decreased by 10 % in most cases. For example, the RRMSE was reduced from 19.26 % to 5.50 % after mitigating the mismatch between the measured and actual solar irradiance, when the solar zenith angle was 40° and viewing zenith angle was 30° in the forward solar principal plane. Even at the nadir observation, the RRMSE was also reduced from 12.84 % to 5.64 %. In summary, MFLD can effectively mitigate the irradiance mismatch effect on the retrieval of RSIF. These results will improve our interpretation of the relationship between GPP and RSIF at different observation directions.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114496"},"PeriodicalIF":11.1,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142599132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evaluation of runoff variability in transboundary basins over High Mountain Asia: Multi-dataset merging based on satellite gravimetry constraint 亚洲高山跨界流域径流变异性评估：基于卫星重力测量约束的多数据集合并

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-11 DOI: 10.1016/j.rse.2024.114493

Jiashuang Jiao , Yuanjin Pan , Xiaoming Cui , Hussein A. Mohasseb , Hao Ding

Runoff variability in glacierized transboundary river basins over High Mountain Asia (HMA) directly affects the stability of water supply for more than one billion people in Asia. However, limited by insufficient in-situ gauges and imprecise hydrological model output, it is still a challenge to accurately monitor and comprehensively analyze the HMA runoff change. In this paper, we construct a water budget closure test of water balance equation based on satellite gravimetry constraints to assess the accuracy of hydrological dataset outputs, and propose a multi-dataset merging method to evaluate runoff variability in ten HMA transboundary basins over the past two decades. Results show that the runoff quantified by the hydrological dataset has relatively maximum uncertainty compared to precipitation and evapotranspiration. The performance of the reconstructed terrestrial water storage change (TWSC) from hydrological dataset varies with basins, and the maximum Nash-Sutcliffe Efficiency (NSE) value ranges from 0.31 to 0.94. Nevertheless, the current hydrological dataset struggles to accurately reconstruct the interannual and annual variability of TWSC, with the maximum cyclostationary NSE (NSEc) value ranging from −1.07 to 0.24. Runoff change in HMA exhibits both overall stability and regional climatic condition-related spatial heterogeneity. A significant downstream change-driven increase trend of runoff occurs in Indus Basin (0.2 ± 0.1 mm/mon/yr), while Brahmaputra Basin (−0.5 ± 0.4 mm/mon/yr) and Salween Basin (−0.4 ± 0.2 mm/mon/yr) show significant runoff decrease trends driven by upstream and downstream changes, respectively. Climate change has exacerbated the instability of runoff in the arid basins over northern HMA, leading to evident increase in annual amplitude. Furthermore, negative correlation is found between temperature and runoff at the interannual scale, especially in Ganges Basin (−19.73 ± 12.53 Gt/month per °C) and Mekong Basin (−17.46 ± 9.43 Gt/month per °C). Our multi-dataset merging methodology can improve the reliability of using global hydrological datasets to quantify runoff variability in poorly in-situ gauged regions, and may also be applicable to the evaluation of precipitation and evapotranspiration.

亚洲高山冰川化跨境河流流域（HMA）的径流变化直接影响着亚洲十多亿人口的供水稳定性。然而，受限于原位测站的不足和水文模型输出的不精确，准确监测和全面分析亚洲高山地区径流变化仍是一项挑战。本文基于卫星重力测量约束条件，构建了水分平衡方程的水预算闭合检验，以评估水文数据集输出的准确性，并提出了一种多数据集合并方法，以评估过去 20 年间 10 个 HMA 跨界流域的径流变化。结果表明，与降水量和蒸散量相比，水文数据集量化的径流具有相对最大的不确定性。根据水文数据集重建的陆地蓄水变化（TWSC）的性能因流域而异，最大纳什-苏特克利夫效率（NSE）值在 0.31 到 0.94 之间。然而，目前的水文数据集难以准确重建总水量变化的年际和年度变化，最大周期性 NSE（NSEc）值在-1.07 到 0.24 之间。HMA 的径流变化既表现出整体稳定性，又表现出与区域气候条件相关的空间异质性。印度河流域（0.2±0.1 毫米/月/年）出现了明显的下游变化驱动的径流增加趋势，而雅鲁藏布江流域（-0.5±0.4 毫米/月/年）和萨尔温江流域（-0.4±0.2 毫米/月/年）则分别出现了明显的上游和下游变化驱动的径流减少趋势。气候变化加剧了哈马河北部干旱盆地径流的不稳定性，导致年幅值明显增大。此外，在年际尺度上，温度与径流之间呈负相关，尤其是在恒河流域（-19.73 ± 12.53 Gt/月/℃）和湄公河流域（-17.46 ± 9.43 Gt/月/℃）。我们的多数据集合并方法可提高使用全球水文数据集量化现场测量条件较差地区径流变化的可靠性，也可用于降水和蒸散的评估。

{"title":"Evaluation of runoff variability in transboundary basins over High Mountain Asia: Multi-dataset merging based on satellite gravimetry constraint","authors":"Jiashuang Jiao , Yuanjin Pan , Xiaoming Cui , Hussein A. Mohasseb , Hao Ding","doi":"10.1016/j.rse.2024.114493","DOIUrl":"10.1016/j.rse.2024.114493","url":null,"abstract":"<div><div>Runoff variability in glacierized transboundary river basins over High Mountain Asia (HMA) directly affects the stability of water supply for more than one billion people in Asia. However, limited by insufficient in-situ gauges and imprecise hydrological model output, it is still a challenge to accurately monitor and comprehensively analyze the HMA runoff change. In this paper, we construct a water budget closure test of water balance equation based on satellite gravimetry constraints to assess the accuracy of hydrological dataset outputs, and propose a multi-dataset merging method to evaluate runoff variability in ten HMA transboundary basins over the past two decades. Results show that the runoff quantified by the hydrological dataset has relatively maximum uncertainty compared to precipitation and evapotranspiration. The performance of the reconstructed terrestrial water storage change (TWSC) from hydrological dataset varies with basins, and the maximum Nash-Sutcliffe Efficiency (NSE) value ranges from 0.31 to 0.94. Nevertheless, the current hydrological dataset struggles to accurately reconstruct the interannual and annual variability of TWSC, with the maximum cyclostationary NSE (NSEc) value ranging from −1.07 to 0.24. Runoff change in HMA exhibits both overall stability and regional climatic condition-related spatial heterogeneity. A significant downstream change-driven increase trend of runoff occurs in Indus Basin (0.2 ± 0.1 mm/mon/yr), while Brahmaputra Basin (−0.5 ± 0.4 mm/mon/yr) and Salween Basin (−0.4 ± 0.2 mm/mon/yr) show significant runoff decrease trends driven by upstream and downstream changes, respectively. Climate change has exacerbated the instability of runoff in the arid basins over northern HMA, leading to evident increase in annual amplitude. Furthermore, negative correlation is found between temperature and runoff at the interannual scale, especially in Ganges Basin (−19.73 ± 12.53 Gt/month per °C) and Mekong Basin (−17.46 ± 9.43 Gt/month per °C). Our multi-dataset merging methodology can improve the reliability of using global hydrological datasets to quantify runoff variability in poorly in-situ gauged regions, and may also be applicable to the evaluation of precipitation and evapotranspiration.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114493"},"PeriodicalIF":11.1,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142599131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evaluating the wilderness status of long-distance trails in the United States - Exploring the potential of SDGSAT-1 glimmer imager data 评估美国长途步道的荒野状态--探索 SDGSAT-1 微光成像仪数据的潜力

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-11 DOI: 10.1016/j.rse.2024.114499

Liding Wang , Mingyang Lv , Changyong Dou , Yue Cao , Steve Carver , Xiancai Lu , Shaochun Dong , Siming Deng , Huadong Guo

Long-distance hiking trails worldwide serve as vital ‘threads’ connecting vast wilderness areas, offering unique opportunities to evaluate progress toward the United Nations' Sustainable Development Goals (SDGs). However, their extensive lengths pose challenges for data collection, limiting their potential use in sustainable development research. Remote sensing technologies, such as high-spatial-resolution and color glimmer imager data from SDGSAT-1, hold promise in addressing these challenges. This study focuses on seven prominent U.S. long-distance trails: the Appalachian Trail, Arizona National Scenic Trail, Buckeye Trail, Hayduke Trail, Ice Age National Scenic Trail, Pacific Crest Trail, and Pacific Northwest Trail, along with 20 km buffer zones surrounding each trail. By integrating glimmer and population data, we introduce a method to quantify human populations within these wilderness areas. Anthropogenic indicators, including population density, land use, grazing intensity, and transportation networks, are used to develop a wilderness evaluation methodology, employing an enhanced human footprint index. Our findings offer a comparative assessment of the wilderness conditions across the selected trails, providing insights into varying levels of human impact and identifying areas where conservation efforts are most urgently needed.

世界各地的长距离徒步旅行路线是连接广大荒野地区的重要 "纽带"，为评估联合国可持续发展目标（SDGs）的进展情况提供了独特的机会。然而，这些徒步旅行线路的漫长长度给数据收集带来了挑战，限制了它们在可持续发展研究中的潜在用途。遥感技术，如 SDGSAT-1 提供的高空间分辨率和彩色微光成像仪数据，有望应对这些挑战。本研究重点关注美国七条著名的长途步道：阿巴拉契亚步道、亚利桑那国家风景步道、布基耶步道、海杜克步道、冰河时期国家风景步道、太平洋山脊步道和西北太平洋步道，以及每条步道周围 20 公里的缓冲区。通过整合微光和人口数据，我们引入了一种方法来量化这些荒野区域内的人口数量。包括人口密度、土地使用、放牧强度和交通网络在内的人为指标被用于开发荒野评估方法，并采用了增强型人类足迹指数。我们的研究结果对所选路径的荒野状况进行了比较评估，深入了解了不同程度的人类影响，并确定了最迫切需要保护的区域。

{"title":"Evaluating the wilderness status of long-distance trails in the United States - Exploring the potential of SDGSAT-1 glimmer imager data","authors":"Liding Wang , Mingyang Lv , Changyong Dou , Yue Cao , Steve Carver , Xiancai Lu , Shaochun Dong , Siming Deng , Huadong Guo","doi":"10.1016/j.rse.2024.114499","DOIUrl":"10.1016/j.rse.2024.114499","url":null,"abstract":"<div><div>Long-distance hiking trails worldwide serve as vital ‘threads’ connecting vast wilderness areas, offering unique opportunities to evaluate progress toward the United Nations' Sustainable Development Goals (SDGs). However, their extensive lengths pose challenges for data collection, limiting their potential use in sustainable development research. Remote sensing technologies, such as high-spatial-resolution and color glimmer imager data from SDGSAT-1, hold promise in addressing these challenges. This study focuses on seven prominent U.S. long-distance trails: the Appalachian Trail, Arizona National Scenic Trail, Buckeye Trail, Hayduke Trail, Ice Age National Scenic Trail, Pacific Crest Trail, and Pacific Northwest Trail, along with 20 km buffer zones surrounding each trail. By integrating glimmer and population data, we introduce a method to quantify human populations within these wilderness areas. Anthropogenic indicators, including population density, land use, grazing intensity, and transportation networks, are used to develop a wilderness evaluation methodology, employing an enhanced human footprint index. Our findings offer a comparative assessment of the wilderness conditions across the selected trails, providing insights into varying levels of human impact and identifying areas where conservation efforts are most urgently needed.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114499"},"PeriodicalIF":11.1,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142599133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evaluation of Himawari-8/AHI land surface reflectance at mid-latitudes using LEO sensors with off-nadir observation 利用低地轨道传感器对中纬度地区的 Himawari-8/AHI 陆面反射率进行离空观测评估

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-11 DOI: 10.1016/j.rse.2024.114491

Beichen Zhang , Kazuhito Ichii , Wei Li , Yuhei Yamamoto , Wei Yang , Ram C. Sharma , Hiroki Yoshioka , Kenta Obata , Masayuki Matsuoka , Tomoaki Miura

Land-surface reflectance (LSR) is a basic physical retrieval in terrestrial monitoring. The potential for high-frequency surface product estimation was evident in third-generation Geostationary Earth Orbit (3rd-GEO) satellites, substantially improving spectral, spatial, and temporal resolutions. Intercomparisons with LSR products from Low Earth Orbit (LEO) satellites have been employed as a common way to evaluate the LSRs of GEO satellites. However, in mid-latitude regions, comparing the LSR between two satellites is challenging due to constraints in the sun–target–sensor geometries. In this study, we proposed a method to obtain observations with consistent viewing and illumination conditions aligned with those of the Himawari-8/Advanced Himawari Imager (AHI) at mid-latitudes, by utilizing forward and backward viewing cameras from LEO sensors, such as Terra/Multi-angle Imaging SpectroRadiometer (MISR). The reflectance intercomparison revealed that the estimated AHI LSR closely matched the LSR from MISR in the red and near-infrared (NIR) bands at latitudes higher than 30°N/S during 2018–2019, with correlation coefficient (r) greater than 0.8 and a relative root mean square error (RRMSE) below 25 %. The data accuracy in the NIR bands was higher than in the red band, as indicated by a lower RRMSE. The correlation was also stronger in non-forested regions compared to forested areas, with higher r values. Additionally, screening observation pairs based on the relative azimuth angle (RAA), which assumes rotational symmetry in LSR, was examined and proved effective for GEO–LEO intercomparisons. This RAA-matching criterion enables reflectance intercomparisons across a wide longitude range at mid-latitudes, including areas like mainland China and New Zealand, where ray-matching is not applicable. The reflectance consistency demonstrated by RAA matches was comparable to that of ray matches, although the RAA-matching is constrained by timing due to the solar location. The findings from this study have potential applications for other satellites.

地表反射率（LSR）是陆地监测中的一项基本物理检索。第三代地球静止轨道（3rd-GEO）卫星大幅提高了光谱、空间和时间分辨率，高频地表产品估算的潜力显而易见。与低地球轨道（LEO）卫星的 LSR 产品进行相互比较是评估地球同步轨道卫星 LSR 的常用方法。然而，在中纬度地区，由于太阳-目标-传感器几何形状的限制，比较两颗卫星的 LSR 具有挑战性。在这项研究中，我们提出了一种方法，通过利用低地轨道传感器（如 Terra/多角度成像光谱辐射计）的前向和后向观测相机，在中纬度地区获得与 Himawari-8/Advanced Himawari Imager (AHI) 一致的观测和照明条件。反射比对结果显示，2018-2019年期间，在北纬30度/南纬30度以上的红外和近红外波段，估计的AHI LSR与MISR的LSR密切吻合，相关系数（r）大于0.8，相对均方根误差（RRMSE）低于25%。近红外波段的数据准确性高于红色波段，这体现在相对均方根误差（RRMSE）较低。与森林地区相比，非森林地区的相关性也更强，r 值更高。此外，还研究了基于相对方位角（RAA）的观测对筛选方法，该方法假定了 LSR 的旋转对称性，并被证明对 GEO-LEO 相互比较有效。这种相对方位角匹配标准能够在中纬度广泛的经度范围内进行反射率相互比较，包括中国大陆和新西兰等不适用射线匹配的地区。RAA 匹配所显示的反射率一致性与射线匹配不相上下，尽管 RAA 匹配受到太阳位置造成的时间限制。这项研究的结果有可能应用于其他卫星。

{"title":"Evaluation of Himawari-8/AHI land surface reflectance at mid-latitudes using LEO sensors with off-nadir observation","authors":"Beichen Zhang , Kazuhito Ichii , Wei Li , Yuhei Yamamoto , Wei Yang , Ram C. Sharma , Hiroki Yoshioka , Kenta Obata , Masayuki Matsuoka , Tomoaki Miura","doi":"10.1016/j.rse.2024.114491","DOIUrl":"10.1016/j.rse.2024.114491","url":null,"abstract":"<div><div>Land-surface reflectance (LSR) is a basic physical retrieval in terrestrial monitoring. The potential for high-frequency surface product estimation was evident in third-generation Geostationary Earth Orbit (3rd-GEO) satellites, substantially improving spectral, spatial, and temporal resolutions. Intercomparisons with LSR products from Low Earth Orbit (LEO) satellites have been employed as a common way to evaluate the LSRs of GEO satellites. However, in mid-latitude regions, comparing the LSR between two satellites is challenging due to constraints in the sun–target–sensor geometries. In this study, we proposed a method to obtain observations with consistent viewing and illumination conditions aligned with those of the Himawari-8/Advanced Himawari Imager (AHI) at mid-latitudes, by utilizing forward and backward viewing cameras from LEO sensors, such as Terra/Multi-angle Imaging SpectroRadiometer (MISR). The reflectance intercomparison revealed that the estimated AHI LSR closely matched the LSR from MISR in the red and near-infrared (NIR) bands at latitudes higher than 30°N/S during 2018–2019, with correlation coefficient (<em>r</em>) greater than 0.8 and a relative root mean square error (RRMSE) below 25 %. The data accuracy in the NIR bands was higher than in the red band, as indicated by a lower RRMSE. The correlation was also stronger in non-forested regions compared to forested areas, with higher <em>r</em> values. Additionally, screening observation pairs based on the relative azimuth angle (RAA), which assumes rotational symmetry in LSR, was examined and proved effective for GEO–LEO intercomparisons. This RAA-matching criterion enables reflectance intercomparisons across a wide longitude range at mid-latitudes, including areas like mainland China and New Zealand, where ray-matching is not applicable. The reflectance consistency demonstrated by RAA matches was comparable to that of ray matches, although the RAA-matching is constrained by timing due to the solar location. The findings from this study have potential applications for other satellites.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114491"},"PeriodicalIF":11.1,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142599135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Impact of altimeter-buoy data-pairing methods on the validation of Sentinel-3A coastal significant wave heights 高度计-浮标数据配对方法对验证哨兵-3A 海岸显著波高的影响

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-06 DOI: 10.1016/j.rse.2024.114483

Guillaume Dodet , Grégoire Mureau , Mickaël Accensi , Jean-François Piollé

Sea state information is critical for a broad range of human activities (e.g. shipping, marine energy, marine engineering) most of them being concentrated along the coastal zone. Satellite altimeter records of significant wave heights (SWH) represent the largest source of sea state observations available to date. However, the quality of altimeter observations is reduced in the coastal zone due to surface heterogeneity within the radar signal footprint. Major difficulties to assess the performance of coastal altimetry in the coastal zone are the reduced number of valid altimeter records and the increased sea state variability, which have recently fostered the development of new methods to pair and compare nearby altimeter and buoy data. In this study, we use a high-resolution numerical wave model implemented over the European coastal waters in order to characterize the spatial variability of sea states in the proximity of coastal in situ buoys, we explore different model-based data-pairing methods to account for coastal sea state variability and we assess their impact on the validation of Sentinel-3A 20Hz SWH measurements. Three Sentinel-3A processing modes are considered: the pseudo low rate mode processing, the SAR processing and the Low Resolution with Range Migration Correction (LR-RMC) processing. Our results indicate major impacts of data-pairing methods on the Sentinel-3A coastal validation and reveals the contribution of more frequent low SWH conditions, poorly resolved by radar altimeters, in the coastal zone as an additional source of errors in coastal altimetry.

海况信息对广泛的人类活动（如航运、海洋能源、海洋工程）至关重要，其中大部分活动都集中在沿岸地区。卫星测高仪记录的显著波高（SWH）是目前最大的海况观测资料来源。然而，由于雷达信号覆盖范围内的地表异质性，沿岸带的测高仪观测质量有所下降。要评估沿岸测高在沿岸带的性能，主要的困难是有效测高记录的数量减少和海况变异性的增加，这促使人们开发新的方法来配对和比较附近的测高数据和浮标数据。在这项研究中，我们利用在欧洲沿岸水域实施的高分辨率数值波浪模式来描述沿岸原位浮标附近海况的空间变异性，探索了不同的基于模式的数据配对方法来考虑沿岸海况的变异性，并评估了这些方法对哨兵-3A 20Hz SWH 测量结果验证的影响。我们考虑了三种哨兵-3A 处理模式：伪低速率模式处理、合成孔径雷达处理和低分辨率与距离迁移校正（LR-RMC）处理。我们的结果表明，数据配对方法对哨兵-3A 海岸验证有重大影响，并揭示了雷达测高计不能很好分辨的海岸带更频繁的低 SWH 条件是海岸测高误差的另一个来源。

{"title":"Impact of altimeter-buoy data-pairing methods on the validation of Sentinel-3A coastal significant wave heights","authors":"Guillaume Dodet , Grégoire Mureau , Mickaël Accensi , Jean-François Piollé","doi":"10.1016/j.rse.2024.114483","DOIUrl":"10.1016/j.rse.2024.114483","url":null,"abstract":"<div><div>Sea state information is critical for a broad range of human activities (e.g. shipping, marine energy, marine engineering) most of them being concentrated along the coastal zone. Satellite altimeter records of significant wave heights (SWH) represent the largest source of sea state observations available to date. However, the quality of altimeter observations is reduced in the coastal zone due to surface heterogeneity within the radar signal footprint. Major difficulties to assess the performance of coastal altimetry in the coastal zone are the reduced number of valid altimeter records and the increased sea state variability, which have recently fostered the development of new methods to pair and compare nearby altimeter and buoy data. In this study, we use a high-resolution numerical wave model implemented over the European coastal waters in order to characterize the spatial variability of sea states in the proximity of coastal in situ buoys, we explore different model-based data-pairing methods to account for coastal sea state variability and we assess their impact on the validation of Sentinel-3A 20Hz SWH measurements. Three Sentinel-3A processing modes are considered: the pseudo low rate mode processing, the SAR processing and the Low Resolution with Range Migration Correction (LR-RMC) processing. Our results indicate major impacts of data-pairing methods on the Sentinel-3A coastal validation and reveals the contribution of more frequent low SWH conditions, poorly resolved by radar altimeters, in the coastal zone as an additional source of errors in coastal altimetry.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114483"},"PeriodicalIF":11.1,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142588930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Sensitivity of Sentinel-1 C-band SAR backscatter, polarimetry and interferometry to snow accumulation in the Alps 哨兵 1 号 C 波段合成孔径雷达反向散射、偏振测量和干涉测量对阿尔卑斯山积雪的敏感性

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-06 DOI: 10.1016/j.rse.2024.114477

Jonas-Frederik Jans , Ezra Beernaert , Morgane De Breuck , Isis Brangers , Devon Dunmire , Gabrielle De Lannoy , Hans Lievens

The physical drivers of Sentinel-1 C-band backscatter observations during snow accumulation are still uncertain. To investigate these, backscatter fluctuations (in co-polarization VV, cross-polarization VH, and cross-polarization ratio VH-VV) were temporally and spatially linked to modeled surface (0–10 cm) soil moisture (SM) and soil temperature (T) (here referred to as soil dynamics) and modeled snow depth (SD) and snow water equivalent (SWE) (snow dynamics) in the bare and herbaceous regions of the Alps at a spatial resolution of 1 km. Results demonstrate that, during snow accumulation and at a regional scale, VH and VH-VV variability is primarily influenced by SD and SWE, whereas VV fluctuations are driven by a combination of soil and snow dynamics. At low local incidence angles, VV is driven by snow dynamics rather than by soil dynamics, which results in a decreased sensitivity of VH-VV to snow accumulation, potentially degrading VH-VV based SD retrieval. Additionally, polarimetric and interferometric Sentinel-1 observations are generated to assess their sensitivity to snow dynamics. Results show that polarimetric

α

(from entropy-

α

dual-pol decomposition) and the first Stokes parameter are more sensitive to SD than VH-VV and VV, respectively, suggesting the potential for improved SD retrievals. Finally, results show that interferometric 6-day coherence observations respond to modeled SWE accumulation, with low coherence values after significant SWE accumulation and higher values in case of minor SWE changes.

积雪期间哨兵-1 C 波段反向散射观测的物理驱动因素仍不确定。为了研究这些问题，在阿尔卑斯山裸露和草本植物区，以 1 公里的空间分辨率，将反向散射波动（共偏振 VV、跨偏振 VH 和跨偏振比 VH-VV）与建模的地表（0-10 厘米）土壤湿度（SM）和土壤温度（T）（此处称为土壤动力学）以及建模的雪深（SD）和雪水当量（SWE）（雪动力学）在时间和空间上联系起来。结果表明，在积雪期间和区域范围内，VH 和 VH-VV 变化主要受 SD 和 SWE 的影响，而 VV 波动则由土壤和雪动力学共同驱动。在局部入射角较低的情况下，VV 受雪动力学而非土壤动力学的驱动，这导致 VH-VV 对积雪的敏感性降低，从而有可能降低基于自毁的 VH-VV 检索结果。此外，还生成了偏振和干涉测量哨兵-1 号观测数据，以评估其对积雪动力学的敏感性。结果表明，极坐标α（来自熵-α双极分解）和第一斯托克斯参数对自毁的敏感度分别高于 VH-VV 和 VV，这表明自毁检索有改进的潜力。最后，结果表明，干涉测量的 6 天相干性观测结果对模拟的 SWE 累积有反应，SWE 大量累积时相干性值较低，SWE 变化较小时相干性值较高。

{"title":"Sensitivity of Sentinel-1 C-band SAR backscatter, polarimetry and interferometry to snow accumulation in the Alps","authors":"Jonas-Frederik Jans , Ezra Beernaert , Morgane De Breuck , Isis Brangers , Devon Dunmire , Gabrielle De Lannoy , Hans Lievens","doi":"10.1016/j.rse.2024.114477","DOIUrl":"10.1016/j.rse.2024.114477","url":null,"abstract":"<div><div>The physical drivers of Sentinel-1 C-band backscatter observations during snow accumulation are still uncertain. To investigate these, backscatter fluctuations (in co-polarization VV, cross-polarization VH, and cross-polarization ratio VH-VV) were temporally and spatially linked to modeled surface (0–10 cm) soil moisture (SM) and soil temperature (T) (here referred to as soil dynamics) and modeled snow depth (SD) and snow water equivalent (SWE) (snow dynamics) in the bare and herbaceous regions of the Alps at a spatial resolution of 1 km. Results demonstrate that, during snow accumulation and at a regional scale, VH and VH-VV variability is primarily influenced by SD and SWE, whereas VV fluctuations are driven by a combination of soil and snow dynamics. At low local incidence angles, VV is driven by snow dynamics rather than by soil dynamics, which results in a decreased sensitivity of VH-VV to snow accumulation, potentially degrading VH-VV based SD retrieval. Additionally, polarimetric and interferometric Sentinel-1 observations are generated to assess their sensitivity to snow dynamics. Results show that polarimetric <span><math><mi>α</mi></math></span> (from entropy-<span><math><mi>α</mi></math></span> dual-pol decomposition) and the first Stokes parameter are more sensitive to SD than VH-VV and VV, respectively, suggesting the potential for improved SD retrievals. Finally, results show that interferometric 6-day coherence observations respond to modeled SWE accumulation, with low coherence values after significant SWE accumulation and higher values in case of minor SWE changes.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114477"},"PeriodicalIF":11.1,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142588308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

An in situ approach for validation of canopy chlorophyll fluorescence radiative transfer models using the full emission spectrum 利用全发射光谱验证冠层叶绿素荧光辐射传递模型的现场方法

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-06 DOI: 10.1016/j.rse.2024.114490

Weiwei Liu , Matti Mõttus , Zbyněk Malenovský , Shengwei Shi , Luis Alonso , Jon Atherton , Albert Porcar-Castell

The intensity and spectral properties of solar-induced chlorophyll fluorescence (SIF) carry valuable information on plant photosynthesis and productivity, but are also influenced by leaf and canopy structure. Physically based models provide a quantitative means to investigate how SIF intensity and spectra propagate and scale from the photosystem to the leaf and to the canopy levels. However, the validation of canopy SIF models is limited by the lack of methods that combine direct, independent, and complementary measurements of the full fluorescence spectrum at the leaf and canopy levels. Here, we propose a novel validation approach that combines in situ measurements of leaf and canopy fluorescence spectra. The approach is demonstrated with measurements in a rice crop at two contrasting stages of canopy development. We measured leaf reflectance, transmittance, and fluorescence spectra in situ, and subsequently inverted leaf structural and biochemical parameters and determined the leaf fluorescence quantum efficiency (FQE) using the Fluspect-Cx model. Two FQE inversion methods (Inversion-IIA and Inversion-IIB) were tested for the forward simulation of leaf fluorescence spectra. Leaf fluorescence spectra were then scaled up to the canopy level using 1D, 2D, and 3D radiative transfer schemes (SCOPE, mSCOPE, and DART), and compared with the direct canopy fluorescence spectral observations measured under red, green, blue, and white illumination. The validation results demonstrate that accounting for 3D canopy structure, as in the DART model, is critical to successfully scale the fluorescence spectrum from the leaf to the canopy level, whereas 1D SCOPE or even 2D mSCOPE were unable to fully reproduce the canopy fluorescence spectra. The results also demonstrate that the Inversion-IIB method matches relatively well the measurements with mean relative absolute errors (MRAE) of 20 %, 37 %, and 43 % versus Inversion-IIA with mean relative absolute errors (MRAE) of 62 %, 100 %, and 108 % for DART, mSCOPE, and SCOPE, respectively. We suggest that our validation approach is transferable to other plant species and canopy geometries, providing a means to standardize and evaluate the performance of canopy SIF models and improve our understanding of canopy SIF observations.

太阳诱导叶绿素荧光（SIF）的强度和光谱特性可提供有关植物光合作用和生产力的宝贵信息，但同时也受到叶片和冠层结构的影响。基于物理的模型为研究 SIF 强度和光谱如何从光合系统传播和扩展到叶片和冠层提供了定量方法。然而，由于缺乏对叶片和冠层的全荧光光谱进行直接、独立和互补测量的方法，冠层 SIF 模型的验证受到了限制。在此，我们提出了一种结合叶片和冠层荧光光谱原位测量的新型验证方法。该方法通过对一种水稻作物冠层发育两个不同阶段的测量进行了演示。我们原位测量了叶片反射率、透射率和荧光光谱，随后利用 Fluspect-Cx 模型反演了叶片结构和生化参数并确定了叶片荧光量子效率（FQE）。对两种 FQE 反演方法（反演-IIA 和反演-IIB）进行了测试，以正向模拟叶片荧光光谱。然后使用一维、二维和三维辐射传递方案（SCOPE、mSCOPE 和 DART）将叶片荧光光谱放大到冠层水平，并与在红、绿、蓝和白光照明下直接测量的冠层荧光光谱观测结果进行比较。验证结果表明，考虑三维冠层结构（如 DART 模型）对于成功地将荧光光谱从叶片扩展到冠层至关重要，而一维 SCOPE 甚至二维 mSCOPE 都无法完全再现冠层荧光光谱。结果还表明，反演-IIB 方法与测量结果的匹配度相对较高，DART、mSCOPE 和 SCOPE 的平均相对绝对误差 (MRAE) 分别为 20%、37% 和 43%，而反演-IIA 的平均相对绝对误差 (MRAE) 分别为 62%、100% 和 108%。我们认为，我们的验证方法可应用于其他植物物种和冠层几何形状，从而提供一种方法来标准化和评估冠层 SIF 模型的性能，并提高我们对冠层 SIF 观测结果的理解。

{"title":"An in situ approach for validation of canopy chlorophyll fluorescence radiative transfer models using the full emission spectrum","authors":"Weiwei Liu , Matti Mõttus , Zbyněk Malenovský , Shengwei Shi , Luis Alonso , Jon Atherton , Albert Porcar-Castell","doi":"10.1016/j.rse.2024.114490","DOIUrl":"10.1016/j.rse.2024.114490","url":null,"abstract":"<div><div>The intensity and spectral properties of solar-induced chlorophyll fluorescence (SIF) carry valuable information on plant photosynthesis and productivity, but are also influenced by leaf and canopy structure. Physically based models provide a quantitative means to investigate how SIF intensity and spectra propagate and scale from the photosystem to the leaf and to the canopy levels. However, the validation of canopy SIF models is limited by the lack of methods that combine direct, independent, and complementary measurements of the full fluorescence spectrum at the leaf and canopy levels. Here, we propose a novel validation approach that combines in situ measurements of leaf and canopy fluorescence spectra. The approach is demonstrated with measurements in a rice crop at two contrasting stages of canopy development. We measured leaf reflectance, transmittance, and fluorescence spectra in situ, and subsequently inverted leaf structural and biochemical parameters and determined the leaf fluorescence quantum efficiency (FQE) using the Fluspect-Cx model. Two FQE inversion methods (Inversion-IIA and Inversion-IIB) were tested for the forward simulation of leaf fluorescence spectra. Leaf fluorescence spectra were then scaled up to the canopy level using 1D, 2D, and 3D radiative transfer schemes (SCOPE, mSCOPE, and DART), and compared with the direct canopy fluorescence spectral observations measured under red, green, blue, and white illumination. The validation results demonstrate that accounting for 3D canopy structure, as in the DART model, is critical to successfully scale the fluorescence spectrum from the leaf to the canopy level, whereas 1D SCOPE or even 2D mSCOPE were unable to fully reproduce the canopy fluorescence spectra. The results also demonstrate that the Inversion-IIB method matches relatively well the measurements with mean relative absolute errors (MRAE) of 20 %, 37 %, and 43 % versus Inversion-IIA with mean relative absolute errors (MRAE) of 62 %, 100 %, and 108 % for DART, mSCOPE, and SCOPE, respectively. We suggest that our validation approach is transferable to other plant species and canopy geometries, providing a means to standardize and evaluate the performance of canopy SIF models and improve our understanding of canopy SIF observations.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114490"},"PeriodicalIF":11.1,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142592604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Assessment of an Adaptive Subwaveform Coastal Retracker (ASCR) over global coastal oceans for SAR altimetry 评估用于合成孔径雷达测高的全球沿岸海洋自适应子波形海岸再跟踪器 (ASCR)

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-05 DOI: 10.1016/j.rse.2024.114495

Fukai Peng , Xiaoli Deng , Yuzhong Shen

To improve the data availability of SAR mode altimeters in coastal zones, we propose a new Adaptive Subwaveform Coastal Retracker (ASCR) and include the empirical coastal retracker ITAS (Improved Threshold Adaptive Subwaveform) and the full-waveform coastal retracker MSCR (Modified SAMOSA+ Coastal Retracker) for comparison in this study. The Sentinel-3A/B altimeter data during the period between January 2020 and December 2022 are reprocessed by these coastal retrackers. The performance of the coastal retrackers, as well as the official Ocean retracker, is intensively assessed over global coastal oceans within 100 km to the coastline. The results show that the coastal retrackers outperform the official Ocean retracker in the 0–20 km distance band, with the data availability increased by up to 7 %, which is statistically significant considering the large amount of coastal sea level data. The ASCR retracker achieves overall better performance than both ITAS and MSCR retrackers. The power spectrum analysis further demonstrates that the noise level within 5 km to the coast is about 35 % higher than that offshore. Moreover, about 6 %–20 % of data loss is observed in the same distance band, which may be because the on-board altimeter fails to record the ocean returns reflected from the nadir sea surface. It is also found that the track-coastline angle is an important factor affecting the data quality of SAR-mode altimeters within the last 10 km to the coast. Finally, the crossover analysis and validation against tide gauges prove that the coastal retrackers can achieve better or at least comparable data quality with official Ocean retracker over global coastal oceans.

为了提高沿岸区域合成孔径雷达模式高度计的数据可用性，我们提出了一种新的自适应子波形沿岸回轨器（ASCR），并将经验沿岸回轨器 ITAS（改进阈值自适应子波形）和全波形沿岸回轨器 MSCR（修正 SAMOSA+沿岸回轨器）纳入本研究进行比较。对 2020 年 1 月至 2022 年 12 月期间的 "哨兵-3A/B "高度计数据，由这些沿岸重新跟踪器进行重新处理。在距海岸线 100 公里以内的全球沿岸海域，对沿岸自动跟踪仪和官方海洋自动跟踪仪的性能进行了深入评估。结果表明，在 0-20 公里距离范围内，沿岸自动跟踪仪的性能优于官方海洋自动跟踪仪，数据可用性提高了 7%。ASCR 自动跟踪仪的总体性能优于 ITAS 和 MSCR 自动跟踪仪。功率谱分析进一步表明，距海岸 5 公里范围内的噪声水平比离岸高出约 35%。此外，在同一距离频段内，观测到约 6%-20% 的数据丢失，这可能是由于机载高度计未能记录从天底海面反射的海洋回波。研究还发现，在距海岸最后 10 公里范围内，轨道与海岸线的夹角是影响合成孔径雷达模式高度计数据质量的一个重要因素。最后，对照验潮仪进行的交叉分析和验证证明，在全球沿岸海域，沿岸自动跟踪仪可以获得更好的或至少与官方海洋自动跟踪仪相当的数据质量。

{"title":"Assessment of an Adaptive Subwaveform Coastal Retracker (ASCR) over global coastal oceans for SAR altimetry","authors":"Fukai Peng , Xiaoli Deng , Yuzhong Shen","doi":"10.1016/j.rse.2024.114495","DOIUrl":"10.1016/j.rse.2024.114495","url":null,"abstract":"<div><div>To improve the data availability of SAR mode altimeters in coastal zones, we propose a new Adaptive Subwaveform Coastal Retracker (ASCR) and include the empirical coastal retracker ITAS (Improved Threshold Adaptive Subwaveform) and the full-waveform coastal retracker MSCR (Modified SAMOSA+ Coastal Retracker) for comparison in this study. The Sentinel-3A/B altimeter data during the period between January 2020 and December 2022 are reprocessed by these coastal retrackers. The performance of the coastal retrackers, as well as the official Ocean retracker, is intensively assessed over global coastal oceans within 100 km to the coastline. The results show that the coastal retrackers outperform the official Ocean retracker in the 0–20 km distance band, with the data availability increased by up to 7 %, which is statistically significant considering the large amount of coastal sea level data. The ASCR retracker achieves overall better performance than both ITAS and MSCR retrackers. The power spectrum analysis further demonstrates that the noise level within 5 km to the coast is about 35 % higher than that offshore. Moreover, about 6 %–20 % of data loss is observed in the same distance band, which may be because the on-board altimeter fails to record the ocean returns reflected from the nadir sea surface. It is also found that the track-coastline angle is an important factor affecting the data quality of SAR-mode altimeters within the last 10 km to the coast. Finally, the crossover analysis and validation against tide gauges prove that the coastal retrackers can achieve better or at least comparable data quality with official Ocean retracker over global coastal oceans.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114495"},"PeriodicalIF":11.1,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142588303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Exploring the potential of SAR and terrestrial and airborne LiDAR in predicting forest floor spectral properties in temperate and boreal forests 探索合成孔径雷达、陆地和机载激光雷达在预测温带和北方森林林地光谱特性方面的潜力

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-03 DOI: 10.1016/j.rse.2024.114486

Audrey Mercier , Mari Myllymäki , Aarne Hovi , Daniel Schraik , Miina Rautiainen

Forest floor vegetation plays a crucial role in ecosystem processes of temperate and boreal forests. Remote sensing offers a valuable tool to characterize the forest floor through reflectance spectra. While passive optical airborne and satellite data have been used to map spectral properties of forest understory, these sensors are limited by cloud cover, especially in high latitudes. To date, LiDAR and SAR have not been explored for this application even though their data are less dependent on illumination conditions and provide information on tree canopy structure and tree distribution which is connected to forest floor properties. We investigated active remote sensing techniques to establish links between forest structure and spectral properties of forest floor across European temperate, hemiboreal and boreal forest ecosystems. First, in the exploratory part, the research question was : Which forest structure metrics are connected to the spectral properties of the forest floor? Next, our predictive part focused on: What is the potential of (1) terrestrial laser scanning (TLS) data, (2) airborne laser scanning data, (3) satellite-borne SAR data, and (4) these data sources combined to predict forest floor spectral properties? Our results revealed that nine forest structure metrics were potentially associated with forest floor reflectance. We identified TLS-derived clumping index and SAR-derived VV backscatter coefficient and VH/VV ratio as significantly connected to forest floor reflectance in certain Sentinel-2 spectral bands. Overall, the active remote sensors achieved the best predictions for forest floor reflectance in red-edge, near-infrared and shortwave infrared regions. Using data from all three sensors together to predict the forest floor spectra yielded better results than using any of the sensors alone. When data from a single sensor were used, the highest prediction accuracies for forest floor reflectance in the red-edge and near-infrared regions were achieved with SAR data, and in the shortwave infrared region with either SAR or TLS data. In the future, the accuracy of predicting forest floor characteristics in temperate and boreal forests could benefit from a synergy of passive and active technologies.

林地植被在温带和北方森林的生态系统过程中发挥着至关重要的作用。遥感技术为通过反射光谱来描述林下植被提供了宝贵的工具。虽然被动光学机载和卫星数据已被用于绘制林下植被的光谱特性图，但这些传感器受到云层覆盖的限制，尤其是在高纬度地区。迄今为止，尽管激光雷达和合成孔径雷达的数据对光照条件的依赖性较低，并能提供与林下特性相关的树冠结构和树木分布信息，但它们尚未被应用于这一领域。我们研究了主动遥感技术，以建立欧洲温带、半寒带和寒带森林生态系统中森林结构与林地光谱特性之间的联系。首先，在探索部分，研究问题是：哪些森林结构指标与林地的光谱特性相关？其次，我们的预测部分侧重于(1) 地面激光扫描数据 (TLS)、(2) 机载激光扫描数据、(3) 星载合成孔径雷达数据以及 (4) 这些数据源结合起来预测林地光谱特性的潜力有多大？我们的研究结果表明，有九种森林结构指标可能与林地反射率有关。我们发现，在哨兵-2 的某些光谱波段中，TLS 导出的团聚指数和 SAR 导出的 VV 后向散射系数和 VH/VV 比值与林地反射率有显著关联。总体而言，主动遥感器在红边、近红外和短波红外区域对林地反射率的预测效果最佳。同时使用三个传感器的数据来预测林地光谱，比单独使用任何一个传感器的结果都要好。使用单一传感器的数据时，红边和近红外区域的林地反射率预测精度最高的是合成孔径雷达数据，短波红外区域的林地反射率预测精度最高的是合成孔径雷达或 TLS 数据。未来，温带和北方森林的林地特征预测精度将受益于被动和主动技术的协同作用。

{"title":"Exploring the potential of SAR and terrestrial and airborne LiDAR in predicting forest floor spectral properties in temperate and boreal forests","authors":"Audrey Mercier , Mari Myllymäki , Aarne Hovi , Daniel Schraik , Miina Rautiainen","doi":"10.1016/j.rse.2024.114486","DOIUrl":"10.1016/j.rse.2024.114486","url":null,"abstract":"<div><div>Forest floor vegetation plays a crucial role in ecosystem processes of temperate and boreal forests. Remote sensing offers a valuable tool to characterize the forest floor through reflectance spectra. While passive optical airborne and satellite data have been used to map spectral properties of forest understory, these sensors are limited by cloud cover, especially in high latitudes. To date, LiDAR and SAR have not been explored for this application even though their data are less dependent on illumination conditions and provide information on tree canopy structure and tree distribution which is connected to forest floor properties. We investigated active remote sensing techniques to establish links between forest structure and spectral properties of forest floor across European temperate, hemiboreal and boreal forest ecosystems. First, in the exploratory part, the research question was : Which forest structure metrics are connected to the spectral properties of the forest floor? Next, our predictive part focused on: What is the potential of (1) terrestrial laser scanning (TLS) data, (2) airborne laser scanning data, (3) satellite-borne SAR data, and (4) these data sources combined to predict forest floor spectral properties? Our results revealed that nine forest structure metrics were potentially associated with forest floor reflectance. We identified TLS-derived clumping index and SAR-derived VV backscatter coefficient and VH/VV ratio as significantly connected to forest floor reflectance in certain Sentinel-2 spectral bands. Overall, the active remote sensors achieved the best predictions for forest floor reflectance in red-edge, near-infrared and shortwave infrared regions. Using data from all three sensors together to predict the forest floor spectra yielded better results than using any of the sensors alone. When data from a single sensor were used, the highest prediction accuracies for forest floor reflectance in the red-edge and near-infrared regions were achieved with SAR data, and in the shortwave infrared region with either SAR or TLS data. In the future, the accuracy of predicting forest floor characteristics in temperate and boreal forests could benefit from a synergy of passive and active technologies.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114486"},"PeriodicalIF":11.1,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Polygon-Informed Cross-Track Altimetry (PICTA): Estimating river water level profiles with the Sentinel-6 altimeter 多边形信息交叉轨道测高（PICTA）：利用哨兵-6 高度计估算河流水位剖面

IF 11.1 1区地球科学 Q1 ENVIRONMENTAL SCIENCES

Remote Sensing of Environment

Pub Date : 2024-11-01 DOI: 10.1016/j.rse.2024.114479

Frithjof Ehlers , Cornelis Slobbe , Florian Schlembach , Marcel Kleinherenbrink , Martin Verlaan

Traditionally, nadir-looking satellite radar altimeters provide water levels of rivers only at intersections with the satellite’s ground track, called virtual stations. These observations have limited spatial coverage because such cross-overs are sparse, depending on the altimeter’s orbit. In this work, we introduce the novel concept of Polygon-Informed Cross-Track Altimetry (PICTA), enabling accurate estimation of water levels at cross-track distances — for as long as the target’s signal is recorded in the altimeter’s range window. Using fully-focused SAR data from the Sentinel-6 altimetry mission, we demonstrate how the new approach can provide detailed river water level profiles over a ground swath of about 14 km cross-track width and with an along-track resolution as fine as 10 m. On the one hand, this marks a drastic improvement in the number of available measurements when compared to the virtual station approach, on the other hand, for the first time, water surface slopes and level variations along the river, caused by rapids, dams, and sluices, can be directly observed using a nadir radar altimeter. The validation over two river segments in France reveals biases as low as

\pm 4

cm and random errors on the order of 3–8 cm at 30 m along-track resolution. The new PICTA concept can potentially be generalized to other targets, such as lakes or even coastlines.

传统上，天底面卫星雷达测高计仅在与卫星地面轨道的交汇处（称为虚拟站）提供河流水位。这些观测数据的空间覆盖范围有限，因为根据测高仪的轨道，这种交叉点很稀疏。在这项工作中，我们引入了新颖的多边形信息交叉轨道测高（PICTA）概念，只要目标信号记录在测高仪的测距窗口内，就能在交叉轨道距离上准确估算水位。利用哨兵-6测高任务中的全聚焦合成孔径雷达数据，我们展示了新方法如何在约 14 千米跨轨宽度的地面范围内提供详细的河流水位剖面图，沿轨分辨率精细至 10 米。一方面，与虚拟站方法相比，这标志着可用测量数据数量的大幅增加；另一方面，利用天底雷达测高仪，可以首次直接观测到由急流、水坝和水闸引起的沿河水面坡度和水位变化。在法国的两个河段进行的验证显示，在 30 米的沿线分辨率下，偏差低至 ±4±4 厘米，随机误差约为 3-8 厘米。新的 PICTA 概念有可能推广到其他目标，如湖泊甚至海岸线。

{"title":"Polygon-Informed Cross-Track Altimetry (PICTA): Estimating river water level profiles with the Sentinel-6 altimeter","authors":"Frithjof Ehlers , Cornelis Slobbe , Florian Schlembach , Marcel Kleinherenbrink , Martin Verlaan","doi":"10.1016/j.rse.2024.114479","DOIUrl":"10.1016/j.rse.2024.114479","url":null,"abstract":"<div><div>Traditionally, nadir-looking satellite radar altimeters provide water levels of rivers only at intersections with the satellite’s ground track, called virtual stations. These observations have limited spatial coverage because such cross-overs are sparse, depending on the altimeter’s orbit. In this work, we introduce the novel concept of Polygon-Informed Cross-Track Altimetry (PICTA), enabling accurate estimation of water levels at cross-track distances — for as long as the target’s signal is recorded in the altimeter’s range window. Using fully-focused SAR data from the Sentinel-6 altimetry mission, we demonstrate how the new approach can provide detailed river water level profiles over a ground swath of about 14 km cross-track width and with an along-track resolution as fine as 10 m. On the one hand, this marks a drastic improvement in the number of available measurements when compared to the virtual station approach, on the other hand, for the first time, water surface slopes and level variations along the river, caused by rapids, dams, and sluices, can be directly observed using a nadir radar altimeter. The validation over two river segments in France reveals biases as low as <span><math><mrow><mo>±</mo><mn>4</mn></mrow></math></span> cm and random errors on the order of 3–8 cm at 30 m along-track resolution. The new PICTA concept can potentially be generalized to other targets, such as lakes or even coastlines.</div></div>","PeriodicalId":417,"journal":{"name":"Remote Sensing of Environment","volume":"316 ","pages":"Article 114479"},"PeriodicalIF":11.1,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0