Upcoming Synthetic Aperture Radar (SAR) missions with larger swath like NASA-ISRO Synthetic Aperture Radar (NISAR) (similar to 250 km) requires a large, flat and homogeneous low-background site, free from human-made structures for point targets deployment for calibration. Finding out such a large, flat, homogeneous area devoid of perceived sources of radar clutter is a challenging task. In this regard, Antarctica is a potential site for calibration as it fulfills many of the criteria required for the ideal calibration site and suitable for setting up a corner reflector (CR) network for SAR calibration. This network will help in the calibration study and aid the studies related to Interferometric SAR (InSAR) viz. ice velocity estimation. As a part of this activity, in-house designed and developed CRs were installed near Indian research base stations Maitri and Bharati at Antarctica during the 38th Indian Scientific Expedition to Antarctica (ISEA) during 2018-2019. Corner reflectors were designed keeping in mind the harsh environment of Antarctica, such as high katabatic winds, blizzards, snowfall and low temperature. Temporal and seasonal analysis of radar backscatter data using available Indian Radar Imaging Satellite (RISAT-1) and European SENTINEL-1 SAR satellite over Maitri and Bharati was carried out to find out the suitable CR deployment site. Super-hydrophobic microwave transparent cover was designed and installed over CRs to protect snow accumulation. Hydrophobic radar absorbing materials were installed over central-mount to decrease the background noise due to it. Various tests such as structural analysis of total CR system, thermal analysis of materials and Radar Cross Section (RCS) characterization of CR were done before sending it to Antarctica. Integrated Wide Swath (IW) mode data of Sentinel-1 satellite was used for analyzing time-series response of CR in SAR image. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

The launch of the Sentinel-1B satellite in April 2016 completed the two-satellite synthetic aperture radar (SAR) constellation of the European Copernicus Sentinel-1 mission. The European Space Agency executed the calibration of this sensor during the commissioning phase and an independent calibration by the German Aerospace Center (DLR) in 2016. The calibration parameters must be monitored to assess the stability of the instrument. This study reports the temporal stability assessment of radiometric calibration and image quality parameters of Sentinel-1B SAR data using the corner reflector (CR) array, Surat Basin, Australia. Impulse response functions generated from the CRs in the satellite images were used to derive the image quality parameters. The average radar cross-section difference between estimated and theoretical values (38.40 dB m 2 ) was 0.53 dB m 2 for 1.5 m CRs, which is accordant with the absolute radiometric accuracy specified for the Sentinel-1 SAR system. Derived image quality parameters viz. the mean peak-to-side lobe ratio, mean integrated side lobe ratio, and spatial resolutions in the range and azimuth directions were found to be accordant with the specified value for the Sentinel-1 SAR system. The results indicate the excellent quality of the Sentinel-1B data.

To date, a large number of existing applications in India have used multi-band observations from airborne and spaceborne platforms.New sensors are providing additional capabilities thanks to special aerial missions with the compact airborne spectrographic imager (CASI), the short-wave infrared (SWIR) full spectrum imager (SFSI) and the National Aeronautics and Space Administration's (NASA's) Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG).Opportunities to exploit quantitative spectroscopic signatures and high spatial resolution have garnered great interest among the scientific community, and the success of these missions will rely on accurate calibration.Here we focus on a vicarious calibration experiment conducted for the AVIRIS-NG India campaign.We discuss initial validation results, with descriptions of in situ and remote calibration and measurement protocols, geometric processing with precise position and attitude data, and atmospheric simulations used to validate the remote measurement.A partnership between Indian Space Research Organisation (ISRO) and NASA investigators proved a unique opportunity to assess the empirical variability in results, indicating their sensitivity to modelling choices and assumptions.The vicarious calibration exercise uses multiple radiative transfer models, including MODTRAN 6.0 and a new version of the 6S radiative transfer code, viz.6SV2.1, which is capable of accounting for polarization.

Optimal Estimation (OE) methods can simultaneously estimate surface and atmospheric properties from remote Visible/Shortwave imaging spectroscopy. Simultaneous solutions can improve retrieval accuracy with principled uncertainty quantification for hypothesis testing. While OE has been validated under benign atmospheric conditions, future global missions will observe environments with high aerosol and water vapor loadings. This work addresses the gap with diverse scenes from NASA's Next Generation Airborne Visible Infrared Imaging Spectrometer (AVIRIS-NG) India campaign. We refine atmospheric models to represent variable aerosol optical depths and properties. We quantify retrieval accuracy and information content for both reflectance and aerosols over different surface types, comparing results to in situ and remote references. Additionally, we assess uncertainty of maximum a posteriori solutions using linearized estimates as well as sampling-based inversions that more completely characterize posterior uncertainties. Principled uncertainty quantification can combine multiple spacecraft data products while preventing local environmental biases in future global investigations.

This study presents the results obtained from image quality assessment of Radar Imaging SATellite (RISAT-1). Image quality parameters such as spatial resolution, peak to sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) are calculated by the analysis of impulse response function (IRF) of the point target. The study is carried out to assess temporal stability and consistency of image quality parameters obtained from analysis of IRF of 44 point targets. The results obtained from this study show that the mean values of the range and azimuth resolution are 2.048 ± 0.081 m and 3.383 ± 0.097 m for RH and 1.981 ± 0.081 m and 3.348 ± 0.076 m for RV, respectively. PSLR/ISLR values for RH channel are obtained as −26.492 dB/−26.823 dB for azimuth and −19.209 dB/−19.921 dB for the range. For RV channel, PSLR/ISLR values are −26.300 dB/−27.572 dB for azimuth and −19.146 dB/−19.827 dB for range.

This study describes the post-launch calibration for visible (VIS) and shortwave infrared (SWIR) bands of Indian National Satellite System (INSAT)-3DR imager over Great Rann of Kutch (GROK) on Day-1 (15th September 2016), when the first time INSAT-3DR Imager camera was switched on. In order to account the characterization of errors and undetermined post-launch changes in sensor spectral response, this calibration activity was performed and extended for its monitoring to Day-56 (since the Day-1; 09th November 2016). A reflectance based technique is used in the present study. The surface reflectance and atmospheric variables were measured over the site as per solar and viewing geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (second simulation of the satellite signal in the solar spectrum) radiative transfer code with the in situ measurements as well as spectral response function of each channel. Preliminary results of the Day-1 vicarious calibration yield gain coefficients of 0.974 and 0.820 for VIS and SWIR channels respectively despite the inhomogeneity of the ground target caused by sufficient sub-surface soil moisture. In extension of the present study, the obtained gain coefficients were 1.001 and 0.9887 for VIS and SWIR, respectively, during Day-56 which indicates the performance of sensor is within the range of pre-launch laboratory calibration.

The INSAT-3D imager (4 km) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on-board Aqua and Terra space-platforms level-2 (1 km) sea surface temperature (SSTskin) product accuracy has been analysed over waters surrounding the Indian subcontinent by indirect comparison method using collocated bulk in-situ measurements (SSTdepth) for 3 years (October 2013-October 2016). Statistical results show that root mean square error of all the three satellites is in range of around 0.600.70 degrees C. Retrieval error is found to be slightly more in case of validation against iQuam data set. INSAT-3D is showing more underestimation with bias ranging from about -0.16 degrees C to -0.20 degrees C than MODIS sensor having bias in range of about 0.06 degrees C to -0.12 degrees C. All the three missions are slightly underestimating over open-ocean with bias ranging in 0-0.17 degrees C. INSAT-3D is significantly underestimating in-situ observations over the Arabian Sea (approximate bias = 0.27 degrees C). Seasonal validation analysis reveals relatively high retrieval error during monsoon season than premonsoon and post-monsoon seasons. MODIS sensor is showing significant underestimation during monsoon with bias ranging from approximately -0.29 degrees C to -0.58 degrees C. Overall, all the three missions are performing similarly well over the study area.

Synthetic aperture radar SAR data used for quantitative temporal and/or spatial analysis requires calibration to ensure that observed pixel values of amplitude and phase can be related to the geophysical parameters of interest. The process of radiometric calibration of SAR images involves comparison of the backscattered radar reflectivity signal from a ground resolution element containing a calibration target of known signal response, such as a corner reflector. In this study, absolute radiometric calibration of RISAT-1 intensity data of fine resolution stripmap-1 FRS-1 and medium resolution ScanSAR MRS mode was carried out by utilizing array of standard point targets of various types triangular trihedral, square trihedral, and dihedral with known radar cross-section deployed prior to satellite overpass with precise azimuth and elevation angles in Desalpar, Rann of Kutch in western India. The derived calibration constants using the integral method were then compared with the values provided in the header file. Deviations in the results are reported in this article. The results obtained show that the difference between the estimated average calibration constants for FRS-1 and MRS mode data with the provided value was found to be within the absolute radiometric accuracy specification of Radar Imaging SATellite RISAT-1. Near-range to far-range difference of 0.1–0.2 dB for HH Horizontal transmit, Horizontal receive polarization and 0.1–0.3 dB for HV Horizontal transmit, Vertical receive polarization was estimated for the same scene using distributed target analysis indicating the stability of calibration for the same scene. This study also concluded that Desalpar site in Rann of Kutch has the potential of being an operational SAR calibration site.

Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30m above mean sea level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD) measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged AOD500 and Ångström exponent (α440–870) values are found to be 0.43±0.26 and 0.69±0.39, respectively. On the seasonal basis, high AOD500 of 0.45±0.30 and 0.61±0.34 along with low α440–870 of 0.41±0.27 and 0.41±0.35 during spring (March–May) and summer (June–August), respectively, suggest the dominance of coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn (AOD500=0.47±0.26, α440–870=1.02±0.27). The volume size distribution and the spectral single-scattering albedo also confirm the presence of coarse-mode aerosols during March–August. An overall dominance of a mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440–870 relationship, while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α′) are also used for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed via the SBDART model is estimated to range from −27.08Wm−2 to −10.74Wm−2 at the top of the atmosphere, from −52.21Wm−2 to −21.71Wm−2 at the surface and from 10.97Wm−2 to 26.54Wm−2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31–0.75Kday−1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.

Long-term measurements of spectral aerosol optical depth (AOD) using sun/sky radiometer for a period of five years (2009-2014) from the remote island location at Kavaratti (KVT; 10.56°N, 72.64°E) in the southern Arabian sea have been analysed. Climatologically, AODs decrease from October to reach maximum of ~0.6 (at 500nm) in March, followed by a sudden fall towards May. Significant modulations of intra-seasonal timescales over this general pattern are noticed due to the changes in the relative strength of distinctively different sources. The corresponding changes in aerosol inversion parameters reveal the presence of coarse-mode aerosols during spring and fine-mode absorbing aerosols in autumn and winter months. An overall dominance of a mixed type of aerosols (~41%) with maximum in winter (~53%) was found via the AOD500 vs. Ångström exponent (α440-870) relationship, while biomass-burning aerosols or thick urban/industrial plumes contribute to ~19%. Spectral dependence of Ångström exponent and aerosol absorbing properties were used to identify the aerosol types and its modification processes. Based on air mass back trajectory analysis, we revealed that the advection of aerosols from Indian subcontinent and western regions plays a major role in modifying the optical properties of aerosols over the observational site. The shortwave aerosol direct radiative forcing estimated via SBDART model ranges from -11.00Wm-2 to -7.38Wm-2, -21.51Wm-2 to -14.33Wm-2 and 3.17Wm-2 and 10.0Wm-2 at top of atmosphere, surface and within the atmosphere, respectively. This atmospheric forcing translates into heating rate of 0.62-1.04Kday-1. Furthermore, the vertical profiles of aerosols and heating rate exhibit significant increase in lower (during winter and autumn) and mid troposphere (during spring). This may cause serious climate implications over Kavaratti with further consequences on cloud microphysics and monsoon rainfall.

In this work, vicarious calibration coefficients for all the four bands (green, red, NIR and SWIR) of Resourcesat-2 AWiFS sensor for four dates during Dec 2013-Nov 2014 and for seven bands (blue, green, red, NIR, SWIR1, SWIR2 and PAN) of OLI sensor onboard Landsat-8 for six dates during Dec 2013-Feb 2015 were estimated using field measured reflectance and measured atmospheric parameters during sensor image acquisition over Rann of Kutch site in Gujarat. The top of atmosphere (TOA) at-satellite radiances for all the bands were simulated using 6S radiative transfer code with field measured reflectance, synchronous atmospheric measurements and respective sensor's spectral response functions as an input. These predicted spectral radiances were compared with the radiances from the respective sensor's image in the respective band over the calibration site. Cross-calibration between the sensors AWiFS and OLI was also attempted using near-simultaneous same day image acquisition. Effect of spectral band adjustment factor was also studied with OLI sensor taken as reference sensor. Results show that the variation in average estimated radiance ratio for the AWiFS sensor was found to be within 10% for all the bands, whereas, for OLI sensor, the variation was found to be within 6% for all the bands except green and SWIR2 for which the variation was 8% and 11% respectively higher than the 5% uncertainty of the OLI sensor specification for TOA spectral radiance. At the 1σ level, red, NIR, SWIR1 and Panchromatic bands of OLI sensor showed close agreement between sensor-measured and vicarious TOA radiance resulting no change in calibration coefficient and hence indicating no sensor degradation. Two sets of near-simultaneous SBAFs were derived from respective ground measured target reflectance profiles and applied to the AWiFS and it was observed that overall, SBAF compensation provides a significant improvement in sensor agreement. The reduction in the difference between AWiFS and OLI measured TOA reflectance was found to be within 1% for green band and within 0.5% for Red band, whereas, maximum difference was observed for NIR band (within 3.4%) after applying SBAF correction.

Aerosols are short-lived with a residual time of about a week in the lower atmosphere and are concentrated around the source of origin. Aerosols are produced by variety of natural processes as well as by anthropogenic activities; it gets distributed in the atmosphere through turbulent mixing as well as transported away from the source of origin and thus results in its large seasonal and spatial variability. In this study, the CIMEL sun-photometer measurements at Kavaratti calibration and validation site are used to characterize the aerosols’ nature at the measurement site. Also, these in-situ measurements are used to validate the satellite sensor derived aerosol optical depth (AOD) parameter. The data analysis shows that the locally generated aerosols are mostly of marine aerosols and other natural aerosols are transported desert dust. The anthropogenic aerosols are transported from mainland and they are found during the pre-monsoon season. Also aerosol measurements for five years (2009 – 2015) are being planned for validating the satellite sensors derived AOD products namely: OceanSat2-OCM2, MODIS-Terra and MODIS-Aqua.

A field experiment was conducted to see the effect of phosphorus (P) and iron (Fe) on protein content in grain and chlorophyll content in leaf of chickpea (Cicer arietinum L.). Four levels of P with four levels of Fe were applied. Increasing P levels increased protein content in grain upto 23.99% in 40 kg P2O5 ha-1 over control (19.09%). But in chlorophyll content at par higher in 40 (2.50 mg g-1) and 60 kg P2O5 ha-1 (2.52 mg g-1) over control (2.30 mg g-1) and 20 kg P2O5 ha-1 (2.38 mg g-1). Application of Fe also increased the protein content with increasing level from 0 to 7.5 kg Fe ha-1. It was lower (23.45%) in control and higher in highest level, which was at par with 5 kg Fe ha-1. In the chlorophyll content maximum increased in 7.5 kg Fe ha-1 over 0, 2.5 and 5 kg Fe ha-1. From the study application of 40 kg P2O5 ha-1 and 7.5 kg Fe ha-1 were found better application than the rest of the treatment.

This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchronising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year’s analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.

The data used in this study is an outcome of visit of Central Monitoring Unit (CMU) for evaluation of Semen Station of Kerala and Chitely Dairy, Maharashtra. To assess the post-thaw motility of frozen semen, frozen straws were taken out randomly from the stored semen and were thawed at 37o C for 15 seconds and motility was recorded. The same samples were subjected to thermal incubation test in water bath at 37o C and progressive motility (%) was recorded at 30 and 60 minutesafter incubation. It was observed that the mean post-thaw motility in exotic breeds (HF and Jersey) was 52.40 per cent followed by 50.85 percent in crossbreds (HF,Jersey, and other crosses).The per cent mean value observed in Indigenous breeds (Tharparkar and Gir) was 45.0 per cent and the difference in post thaw motility was non significant (p<0.05) among breed groups. The overall mean post-thaw motility was 51.02 per cent.Further these thawed samples were incubated at 37o C for 60 minutesand there was consistent reduction in the motility at 30 and 60 minutes. This reduction varied from 6.29 per cent(pure exotic) to 11.25 per cent(indigenous) semen after 30 minutes of incubation and the differences were significant (p<0.05) among breed groups. However, at 60 minutes breed difference in the per cent drop of motility on incubation was non-significant. It was observed that there was no significant difference in the post-thaw motility and reduction in motility after incubation of frozen semen among the evaluated semen stations. Among the semen production stations, the average post- thaw motility of frozen semen varied from 52.70 to 49.70 per cent and motility after 60 minutes of incubation varied from 36.62 to 40.63 per cent, respectively. The results indicated that the reported semen stations are following the Minimum Standard Protocol (MSP) for freezing and thawing and maintaining their semen quality as per the standard guidelines of MSP.

The present paper deals with the retrieval of the atmospheric layer averaged relative humidity profiles using data from the Microwave Humidity Sounder (MHS) onboard the MetOp satellite. The retrieval has been innovatively performed by firstly retrieving humidity for pairs of thick overlapping layers (TOLs) used subsequently to derive humidity for associated thin isolated layer (TIL). A water vapour dependent (WVD) algorithm has been developed and applied to infer the humidity of TOLs. Thus, the retrieved profiles have been finally compared with standard algorithm (NORM). These algorithms have been developed based on radiative transfer simulations and study of sensitivities of MHS channels on humidity of various types of layers (TOL, TIL). The algorithm has been tested with MHS data and validated using concurrent radiosonde as well as NCEP reanalysis data indicating profile errors of ~15% and ~19%, respectively.