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The User Equivalent Range Error (UERE) accuracy of NavIC satellites performs better than 20 m based on operational orbit determination (OD) from sixteen IRIMS one-way range measurements, and two-way range measurements using four IRCDR stations. These stations are geographically located within India and a few outside. The NavIC-OD is carried-out by applying a weighted least square batch estimation algorithm.The present work performs a study to estimate the position instantaneously using trilateration by extending network of tracking stations with a sufficiently Long Baseline Tracking Stations (LBTS) in such a way that minimum four number of LBTS will have simultaneous access to any NavIC satellite. The Gauss–Newton Method is employed to estimate the position instantaneously. Further, LBTS stations tracking data are simulated to enhance the NavIC broadcast ephemeris by carrying out real time OD with Extended Kalman Filter (EKF).

Temperature is responsible for the rise of air parcels in the atmosphere, which in turn impairs the transmission of electromagnetic waves. Therefore, atmospheric stability is a function of the temperature of the rising and sinking air parcel with respect to the environmental air temperature at the lifted condensation level (LCL). Refractivity-based lifted index (RLI), a stability index model, uses an approximate LCL value. This study modifies the RLI using the exact formula of the LCL to obtain a precise modified refractivity-based lifted index (MRLI) model for the computation of refractivity-based atmospheric stability profiles. Two years (2020–2021) reanalysis data of atmospheric parameters (temperature, relative humidity and atmospheric pressure) were obtained from European Centre for Medium-Range Weather Forecasts (ECMWF) satellite for Lagos (6.6018° N, 3.3515° E), Abuja (9.0765° N, 7.3986° E) and Yola (9.2095° N, 12.4782° E) at 500–1000 hPa. RLI and MRLI were analysed at four synoptic hours (0, 6, 12, and 18 h) Local Time (LT). The trend shows that when RLI is negative, MRLI is negative; when RLI becomes less negative, MRLI is less negative, except in some cases where a significant amount of water vapour is observed at 500 hPa. Furthermore, a higher negative MRLI value indicates more environmental moisture and is supportive of convective activity, which implies an unstable atmosphere. MRLI has higher night-time (18–0 h LT) values compared to the daytime (6–12 h LT) due to low temperature and high humidity. Also, MRLI negative value decreases as the altitude increases with seasonal averages of − 97, − 86, and − 83 N-units over Lagos, Abuja, and Yola, respectively. A strong positive relationship was observed between MRLI and RLI, with correlation coefficients of 0.99999 for Lagos, 0.99823 for Abuja, and 0.99765 for Yola. MRLI attempts to lower the approximation error exhibited by RLI values for dry season months over Abuja and Yola.

This paper proposes co-planner waveguide (CPW)-fed modified fractal antennae for wideband and multiband applications. The proposed antennas have a resonance frequency in the range of 24–40 GHz with 40 × 40 mm² dimensions. The corporate CPW (Coplanar Waveguide) feeding technique is integrated with the ring, meander line, and periodic staircase with a slot pattern and augmented by conductive graphene for Electromagnetic Band Gap and Photonic Band Gap structures on the opposite side of the Substrate. This integration significantly enhances antenna performance, manifesting superior radiation properties, increased gain, enhanced directivity, and resonating behavior concerning fractal antennae. The proposed PBG and EBG fractal antennas exhibit peak directivities ranging from 9.95 to 9.48 dBi for different angles (Phi = 0°, Phi = 90°, Theta = 90°) with beam scanning and pencil beam properties, with maximum return losses of 47 dB and 30 dB for PBG and EBG designs, respectively. The covered bandwidths include 26–28 GHz, 28.4–36.3 GHz, and 25–26.5 GHz, 27.7–29.8 GHz, 31–33 GHz, 34.1–40 GHz, compatible with 5G NR bands n257, n258, n259, n260, and n261, and ground-based radio navigation applications. Simulations using CST and validations with vector and spectrum analyzers confirm these results.

A novel Ultra Wide-Band (UWB) frequency reconfigurable filtering antenna (or reconfiltenna) is presented in this research article. In the first step, a stepped-flower-shaped UWB antenna is optimized having a 3.5–14.1 GHz band. In the next step, a UWB filter with two stubs is designed to pass the frequency band from 3 GHz to 11.2 GHz having a stop band (notch) in between them from 5.9 GHz to 7.1 GHz. Then, the filter is merged with the feedline of the UWB antenna. The radiating patch is coupled at the output of the filter forming the filtering antenna or filtenna. This filtenna operates from 3.52 GHz to 10.1 GHz with a notch band of 5.42 GHz to 6.8 GHz. Finally, six PIN diodes are embedded in the stubs of the filter to vary the effective length of the stubs by switching ON/OFF the PIN diodes in different combinations. This variation, in turn, produces a controllable or trackable notch-band. The proposed reconfiltenna carries a small volume of 32 mm × 27 mm × 0.2 mm with a thin photo paper substrate. It produces a maximum gain and efficiency of around 7.54 dBi and 83% respectively. The simulated outcomes are cross-referenced and confirmed through comparison with experimental results.

The present study focuses on the elemental characterization and contribution of prominent sources of particulate matter (PM) in Darjeeling, the high-altitudinal eastern Himalayan station. The concentration of PM₁₀ and PM_2.5 was exceeded the National Ambient Air Quality Standards (NAAQS) for 72% and 83% of the sampling days, respectively. Since the World Health Organization or other government organizations has not set any standards for PM₁, the standards of PM₁₀ and PM_2.5 were considered as benchmarks. The concentration of PM₁ exceeded the NAAQS for PM₁₀ and PM_2.5 on 57% and 85% of the days, respectively. The elemental characterization using wavelength dispersive X-ray fluorescence (WD-XRF) technique identified 21 elements with the dominance of Si, Na, B, Ba, Al, and K in PM₁₀; while, Al, N, and B in PM_2.5 and PM₁. Principal component analysis depicted that biomass burning, fossil fuel combustion, crustal/soil dust, and industrial emissions were identified as primary contributors to PM₁₀; PM_2.5 was substantially attributed to industrial emissions, agricultural activities, biomass burning, vehicular activities and natural sources. Additionally, natural sources and anthropogenic activities like vehicular, agricultural, and industrial emissions, and combustion were identified as the major sources of PM₁ in Darjeeling. The findings of this study could potentially raise awareness among researchers and policymakers, prompting them to develop sustainable strategies in hill regions across the globe.

Seasonal variations in the atmospheric boundary layer over different geographical regions have distinct features due to variations in topography, land cover, and geographical position. This study focuses on Atmospheric boundary layer height (ABLH) characteristics seasonally and diurnally over the Indo-Gangetic Plain (Varanasi) and Coastal region (Goa). The study also emphasizes the relationship between ABLH and associated variables such as surface sensible heat flux (SSHF), surface latent heat flux (SLHF), convective available potential energy (CAPE), and Relative humidity (RH) for pre-monsoon and monsoon season. ECMWF-ERA-5 reanalysis data for the period of 2015 to 2017 were used for the study. ECMWF-ERA-5 reanalysis data was validated with MERRA-2 data using correlation coefficient (r) and Factor of Two (FAC2) value. Validation suggested the reliability of ECMWF-ERA-5 data which showed an r-value of 0.8 and FAC2 value in ≥ 0.5 ≤ 2.0 range with MERRA-2 data. The results showed 1400–1800 m and 1000–1400 m ABLH during pre-monsoon and monsoon respectively over Varanasi while ABLH of 1000–1400 m and 500–700 m was seen over Goa during pre-monsoon and monsoon respectively. The analysis indicated that deeper ABLH was observed over Varanasi than over Goa during both seasons. Further, regression correlation analysis detailed the parameters affecting the ABL height characteristics. Surface heat fluxes showed a stronger correlation with ABLH over Varanasi than over Goa. Regression coefficients for ABLH and surface sensible heat flux (SSHF) were found to be 0.88 and 0.82 during pre-monsoon and monsoon respectively over Varanasi and 0.76 and 0.66 during pre-monsoon and monsoon respectively over Goa. Surface latent heat flux (SLHF) also showed significant regression coefficients of 0.83 and 0.62 over Varanasi and 0.76 and 0.66 over Goa during premonsoon and monsoon respectively. Multivariate regression analysis quantified the effect of independent variables (SSHF, SLHF, CAPE, RH) on the dependent variable (ABLH) by estimating β coefficient. The variables which affected ABLH at a significant level (α = 0.05) were heat fluxes (SSHF and SLHF) and CAPE during pre-monsoon over both regions. Significant contributor to ABL height found to be SLHF over Goa during monsoon. South westerly moist winds and buoyant thermals might have impacted the ABLH over Goa because latent heat flux is highly affected by surface winds and specific humidity gradient at surface and atmosphere. Also, uninterrupted moisture supply along with strong onshore winds strengthen the SLHF. Furthermore, the geographical location of Goa might have amplified the variable effects shaping ABLH during the monsoon. On the other hand, significant contributors were SSHF, SLHF and CAPE over Varanasi during the same season i.e. monsoon.

The shape of a PCB surface, i.e., its topography, influences many functional properties of the designed circuit. In this paper, we propose the utilization of a non-contact, non-invasive, and non-destructive simplified microscopic fringe projection technique for the surface profiling of copper-clad PCBs. Here, a digital micromirror device (DMD) is used to project a high spatial fringe density at the surface of copper-clad PCBs to achieve high-speed profilometry, which can avoid disturbance due to in-field vibrations. Furthermore, the optimal spatial frequency of 70 µm pitch is selected empirically to minimize phase error by comparing the sample’s surface phase map at different spatial frequencies. The experimentally calculated average height using optimal spatial frequency for the central portion of the antenna’s surface is found to be 13.46 µm, and it is well in coordination with the height of 14.72 µm obtained using a standard roughness tester. The qualitative and quantitative experimental results verified the practical applicability of the fringe projection system for measuring the surface profiling of copper-clad PCB.

The present paper outlines the efforts for the range extension of the existing CSIR-NPL micro liquid flow calibration facility (having flow range of (10–1500) mL/h) from 10 mL/h  down to 1 mL/h and its metrological assessment. The major challenges in this study are evaporation, flow rate stability and repeatability. To reduce the evaporation, a small quantity of mineral oil was mixed with distilled water in the collection beaker, forming a thin layer of oil over the beaker water surface, leading to reduced evaporation. For improving the flow stability and repeatability, a high-accuracy syringe pump with a 10 mL syringe and a precision balance of 82 g capacity have been used. The static weighing with standing start and standing finish method has been used for flow measurement. The expanded uncertainty (at k = 2 for approx. 95% confidence level) of the facility is found to be (1.0–0.30) % in the flow range (1–1500) mL/h for both totalized volume and volume flow rate measurements. Thus, CSIR-NPL is now able to maintain NMI status in micro liquid flow measurement.

There is a constant need to regularly calibrate He–Ne laser sources to ensure their precision in various applications. However, such calibration systems are currently not available in Indonesia. For this reason, developing a decent calibration system capable of maintaining He–Ne laser traceability is essential. This paper studies the realization of substitution methods to calibrate stabilized He–Ne lasers. The wavelength of the stabilized He–Ne laser to be calibrated (DUC) and the reference He–Ne laser (Agilent 5519B) were measured by a wavelength meter, Advantest (Q8326), that has sufficient short-time stability. The calculated ratio between both wavelengths was used as a reference value in determining the wavelength of the DUC laser. A calibration of laser head Polytec OPV-503 at 632.8 nm with instability 1.5 × 10⁻⁵, was performed to validate the method. It was found that the DUC has a wavelength of (632.9907 ± 0.0001) nm. The result shows that the calibration system can be used to establish traceability to the SI unit of the metre, particularly for the He–Ne laser with stability greater than 0.0001 nm that we expect to be sufficient for laser displacement interferometer applications, e.g., as the primary standard in vibration calibration.

The present study examined the long–term characteristics and relationship of atmospheric ammonia (NH₃) with other trace gases (NO, NO₂, SO₂ and CO) at highly polluted urban agglomeration of Delhi, India. Measurements of ambient trace gases (NH₃, NO, NO₂, SO₂, and CO) and meteorology were recorded at the observational site of Delhi from 2011–2022. Overall mean mixing ratios  of ambient NH₃, NO, NO₂, SO₂ and CO were 18.9 ± 5.0 ppb, 19.9 ± 4.8 ppb, 19.1 ± 5.3 ppb, 2.15 ± 0.38 ppb, and 1.47 ± 0.42 ppm, respectively during 2011—2022. During study, a significant diurnal and seasonal variation in mixing ratios of NH₃, NO, NO₂, and CO were observed except SO₂ mixing ratio. During all the seasons, the mixing ratios of trace gases were observed higher during nighttime and lower during daytime. Correlation analysis reveals that the higher loading of NO, NO₂ and CO influenced the mixing ratio of NH₃ at the study site of Delhi.