Fusion of altimetry-derived model and ship-borne data in preparation of high-resolution marine gravity determination

Summary Satellite altimetry provides major data sources for marine gravity recovery, and typical altimetry derived models, e.g., DTU21 and SS V32.1, were usually released with 1'x1' gridding interval. Their true resolution is much lower than the nominal ∼2 km level. By contrast, the in-situ ship-borne measurements are considered to have better short-wavelength resolution. In this paper, we aim to propose a new method to fully utilize satellite altimetry data and ship-borne measurements, namely the frequency domain fusion method, and give certain analysis of new method along with two spatial domain fusion methods. Comprehensive analysis is focus on four aspects: gravity signals in fusion images, numerical verifications, power spectra, as well as coherence analysis. Initial evaluation indicates that, firstly, the frequency domain fusion method has advantage in flexibility, since it can autonomously select dominant bands to fuse different datasets. Secondly, the new method retains medium-long wavelength signals from altimetry-derived model and effectively incorporate dominant short-wavelength signals of in-situ measurements, while the spatial domain methods are essentially full-wavelength fusion and inevitably diminish the role of satellite altimetry. To some extent, the new method maximize the positive contribution of satellite altimetry measurements and efficiently exploit the benefits of ship-borne data. Finally, verification experiments were similarly designed in three regions with different amount and ratio of shipborne data to thoroughly evaluate various methods. In two regions with gridded and dense along-cruise ship-borne data, the average accuracy of this frequency domain fusion results is improved by 0.346 mGal and 0.613 mGal, respectively. In a region with sparse ship-borne data, we still recommend using spatial domain fusion methods since the new method is unable to align ship-borne data with model grid. It is concluded from the above analysis that the new method effectively incorporates the short-wavelength signals from ship-borne data into the altimetry-derived gravity field model, and it is significant that the new method maximizes the application of advantageous bands from different data sources.