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An introduction is presented in which the editor discusses articles in the issue on topics including configuration and improvements of the EOS-04 SAR system, challenges in realization of miniaturized C-Band TRiM modules and calibration of the SAR sensor.

Here we provide a brief description of the post-launch data quality evaluation and calibration--validation chain of the SCATSAT-1, the second scatterometers mission of Indian Space Research Organisation. This chain is of absolute importance to monitor the satellite health and its impact on its measurements. It also provides us overview of the suitability of the data for various applications. The results show that the SCATSAT instrument is having nominal behaviour, the measurements are of very high quality and is comparable to the reference mission QuikSCAT. The ocean surface winds derived using SCATSAT-1 are having errors less than 1 m/s and hence it is suitable for all operational meteorological and oceanographic applications. [ABSTRACT FROM AUTHOR]

The article discusses the asymbiotic seed germination and in vitro seedling development of the lady's slipper orchid variety, Paphiopedilum villosum (Lindl.), in India. Also cited are the substantial reduction in the orchid's area of occupancy (AOO) that led to its listing in the International Union for Conservation of Nature (IUCN) Red Data Book, and the use of a combination of media and phytohormones as an effective in vitro propagation of the orchid.

In general, little emphasis is given on the production of medicinal plant species for sustainable harvest and conservation in the understorey of degraded forests. For instance, forests like chir pine which are not managed to grow any medicinal plants, offer an opportunity to produce and conserve native medicinal plants. This article highlights a study focusing on the production of medicinal plants in association with Chir pine forests, involving sustainable management techniques like minimum tillage and selecting suitable aspects for the sustainable harvest and conservation of plants under the canopy of trees. The medicinal plants were grown on three topographical aspects – Northern, North- Western and Western by adopting three tillage depths, viz. minimum (0 cm), medium (up to 10 cm) and deep tillage (up to 15 cm), in open and below tree canopy conditions. From yield and economic point of view, Andrographis paniculata, Mucuna pruriens, Solanum khasianum and Spilanthes acmella were found to be better yielding and more remunerative in comparison to Withania somnifera, Cymbopogon nardus and Ocimum basilicum, when grown outside the tree canopy adopting deep tillage on the Western aspect in Chir pine forests. The study can also be applicable to the other parts of the country to produce and conserve native medicinal plant species using sustainable management techniques like minimum tillage in blank patches or understorey of the degraded forests. [ABSTRACT FROM AUTHOR]

An evaluation for the development work done in the two watersheds, viz. Bunga and Dabkauri in Panchkula District, Haryana was carried out for 2004 and 2007. Satellite digital data of LISS-IV sensor for 2004 and merge product of LISS-III and PAN for 2007 was used. The data was interpreted for their land use/land cover classes for both the years. The data shows that there is an increase of 33.93% in crop land area. There is a substantial decrease of 97.84% in agricultural fallow land, i.e. land without scrub and sparse vegetation on hills also decreased during the period. Dense vegetation area, i.e. forest plantations on the hills and in the Piedmont area was increased. It was observed that a total of 33 water harvesting structures were constructed between 2004 and 2007. [ABSTRACT FROM AUTHOR]

This paper describes a scheme that uses holographic optics for realization of schlieren diffraction interferometer. The interferometer has been realized with single holographic optical element in conjunction with a collimated beam and the focal plane-modifying element. Multiplexing ability of holographic optics also enables simultaneous operation of more than one technique such as schlieren, shadowgraph and interferometric techniques. Combined schemes where one or more techniques could be applied simultaneously are useful for detailed investigations of phenomena like flow of compressible fluids, because each method has its own characteristic strengths and weaknesses. Procedures for the generation of holographic optical element and realization of various schemes have been presented. [ABSTRACT FROM AUTHOR]

The article offers information on the flood events in Assam focusing on a recent flood activity in Kaziranga National Park, Assam, India with the help of remote sensing data. The article mentions the biodiversity of the park and that it is regarded as World Heritage Site by UNESCO. The article provides information on flood modelling with remote sensing data, the use of datasets with the help of radar altimeter, Landsat, and Land-use and land-cover map for the park.

Surface soil moisture (SSM) at high spatial resolution is an essential land parameter for agricultural applications like irrigation mapping, scheduling, crop water stress assessment, etc. However, available satellite derived soil moisture products are inadequate for meeting the requirements of agricultural applications due to coarse scale soil moisture (~10–40 km). In this article, we developed an operational framework for first of its kind sub-km (~500 m) operational soil moisture product over India by utilizing ISRO’s EOS-04 C-band synthetic aperture radar (SAR) data based on active-passive approach. The potential of EOS-04 SAR for sub-km scale is demonstrated and tested over major cropland sites covering highly heterogeneous and dynamic crop conditions in different agro-climatic regions over India which shows a good agreement with in situ datasets with mean ubRMSE, ranging from 0.051 to 0.078 m³ /m³. [ABSTRACT FROM AUTHOR]

The article offers information on the importance of the ocean surface winds for various meteorological and oceanographic applications. It discusses the importance of the study of severe weather events like cyclones, hurricanes and typhoons for assimilation in numerical weather forecast models to improve the forecast, along with information on the SCATSAT-1, a miniature satellite providing weather forecasting launched by the Indian Space Research Organization.

The article focuses on airborne imaging spectroscopy data acquired through hyperspectral campaign with U.S. National Aeronautics & Space Administration's AVIRIS-NG imaging spectrometer on-board Indian Space Research Organisation's B-200 aircraft. Topics discussed include spectral interval with high signal-to-noise ratio over the Indian subtropics; hyperspectral data analysis covering calibration and validation, data processing and retrieval algorithms; and identification of coral macrophytes.

Ravine agro-ecosystems are characterized by degraded gullied lands formed over the years due to several natural and anthropogenic factors, surrounded by the adjacent table lands cultivated for the production of food and fibre for humans and livestock. These potential lands not only support the livelihood of marginal and smallholder farmers, but are host to various plants and grass vegetation providing a cushion to the local environment. A two-way relationship exists between the human settlements and ecosystem services in these agro-ecosystems. While the ravines support plants, grasses and human settlements in these agroecosystems, the same biophysical pressures over time degrade the ecosystem leading to ecosystem services loss, if not managed sustainably. The present pilot study conducted in the Mahi ravines, Gujarat, India, has examined these issues from the local socio-ecology perspectives and suggests management options for participatory management. [ABSTRACT FROM AUTHOR]

In order to observe severe weather conditions during cyclones, thunderstorms, etc., IMAGER instruments on-board INSAT3D/3DR have been built with a flexible scanning feature known as 'rapid scan mode'. Using this feature, the number of scan lines over a given coverage region and the number of repetitions of the selected region can be programmed for scanning. Therefore, to understand the physical processes involved in convective clouds associated with severe weather phenomena, rapid scan of INSAT3DR mode is attempted. It has very high temporal resolution of approximately 4 min and 30 sec. The present study will help in better understanding of the physical processes of severe weather phenomena and in nowcasting. It will also help to improve the accuracy in the NWP model forecast through assimilation of radiances and atmospheric motion wind determined using rapid scan mode. [ABSTRACT FROM AUTHOR]

Determining nearshore bathymetry by traditional surveying methods is a challenging task as it involves huge costs and efforts. Most of the coastal shallowwater zones worldwide either remain unmapped or not updated. Bathymetry estimations from optical satellite imageries have been increasingly implemented as an alternative tool for traditional bathymetry surveys. In this study, we examine the usefulness of freely available, five-day revisit and relatively highresolution Multi Spectral Instruments (MSI) on-board Sentinel-2A and 2B twin satellites. A process workflow has been developed which automatically incorporates a robust atmospheric correction through ACOLITE software and multi-scene compositing of several scenes to improve the reliability and no data gaps. Two study sites in India are explored owing to their variability in submarine morphology. High-resolution bathymetry maps are generated through a log-ratio transform model calibrated with minimal in situ data from the jet ski soundings. The satellite-derived bathymetry obtained has an overall bias of -0.01 and 0.02 m, and root mean square error of 1.09 and 0.93 m respectively, at two study sites up to 15 m depth. The consistency in bathymetry retrieval indicates a potential for automated application for the benefit of operational and scientific studies. These high-resolution maps capture small-scale nearshore features like sandbars and rip channels, which are of prime importance for coastal and beach managers. [ABSTRACT FROM AUTHOR]

In this study we identify a region of submarine groundwater discharge (SGD) near Okha coast, Gujarat, India using thermal infrared remote sensing technique. Observations of brightness temperature (BT) in the thermal infrared spectral region (10.6–11.19 μm) from Landsat-8 satellite in the coastal region showed unique localized cooling in the Arabian Sea during winter. We observed lowering of BT in the range 0.6°– 2.3°C in the coastal region associated with SGD in comparison to sea surface temperature of the ocean during low-tide conditions. Consistent geographical pattern of thermal contrast was observed near the same location (lat. 22°26′54.43″N, long. 69°00′41.67″E) when multi date (11 datasets) thermal data were analysed between 2015 and 2019 in winter. Generally, low-tide conditions show more cooling of ocean surface at the SGD site compared to high-tide conditions, which indicates the process of SGD. Satellite-based assessment was further validated using field- and ship-based measurements. [ABSTRACT FROM AUTHOR]

In this study, a method for retrieving ocean surface wind speed using C-band cross-polarization SAR observations has been outlined. A linear least square technique has been used to develop a Geophysical Model Function (GMF), C2P. The GMF was derived using NRCS observations from RISAT-1 and wind-speed observations from ASCAT. The correlation between observed and simulated NRCS values obtained from C2P was 0.66, with a negative bias of 0.01 dB and the corresponding root mean square difference of 1.13 dB. Subsequently, the developed GMF was tested with 774 RISAT-1 MRS datasets to retrieve wind speed along the Indian coast and also of the tropical cyclone 'Megh'. The measured intensity and radius of maximum wind speed were 30 m s-1 and 16.65 km respectively. Subsequently, the retrieved wind speed was validated with ASCAT wind-speed observations. The statistical comparison of RISAT-1 and ASCAT observed wind speed showed negative biases of 0.90 and 0.34 m s-1 with the corresponding RMSD of 2.11 and 1.77 m s-1 respectively, for CMOD5.N and C2P. The developed GMF C2P showed 16% more accuracy than that of CMOD5.N. [ABSTRACT FROM AUTHOR]

Lagrangian drifters are analogues of particles that are relevant to flow-field characterization and therefore they represent realistic surface currents compared to Eulerian techniques. The use of global navigation satellite system (GNSS) in such drifters with Differential Global Positioning System mode at high frequency (5-10 Hz) sampling and post-processing kinematic results in position estimates with centimeter-level accuracy. In the complex nearshore zone, deploying expensive instruments is a risk due to greater chances of loss. To avoid this, two drifters have been designed and developed using a low-cost Emlid Reach® GNSS receivers, antennae and 'off-the-shelf' PVC components to measure the surface currents. The dimensions of the drifters were optimally chosen to minimize the wind and wave impacts and to increase the subsurface current drag. An analysis of relative position and velocity errors from stationary observations indicates that the drifter can resolve motion accurately with minimal errors of ±1 cm and ±2 cm/s respectively. These drifters were used to measure surf zone currents at the RK Beach, Visakhapatnam during May 2018 and to successfully identify dangerous rip current zones. This study presents the design, development aspects, error analysis and testing of GNSS drifters. Although these drifters are primarily developed to measure the rip current velocities and trajectories in the nearshore zone, they can also be operated in any marine environment like rivers, lakes, estuaries, etc. without change in the design. An extensive study using a fleet of such drifters is required to understand the complex physical processes in the marine environment. [ABSTRACT FROM AUTHOR]

Dual-frequency Synthetic Aperture Radar (SAR) operating in L- and S-band frequencies is one of the primary payloads of the Chandrayaan-2 orbiter. This payload with the capability of imaging in dual frequency (L-band: 24 cm wavelength and S-band: 12 cm wavelength) with full polarimetric mode aims for unambiguous detection, characterization and quantitative estimation of water-ice in permanently shadowed regions over the lunar poles. The payload will address the ambiguities in interpreting high values of circular polarization ratio associated with water-ice observed during previous missions to the Moon through imaging in dual-frequency fully polarimetric SAR mode. Various improved system features such as wide range of resolutions and incidence angles, synchronized Land S-band operations, radiometer mode, are built into the instrument to meet the required science objectives, adhering to stringent mission requirements of low mass, power and data rates. Major scientific objectives of dual-frequency polarimetric SAR payload are: unambiguous detection and quantitative estimation of lunar polar water-ice; estimation of lunar regolith dielectric constant and surface roughness; mapping of lunar geological/morphological features and polar crater floors at high-resolution, and regional- scale mapping of regolith thickness and distribution. [ABSTRACT FROM AUTHOR]

SCATSAT-1 is a continuity mission for the Oceansat-2 scatterometer, OSCAT-1, which provided useful ocean vector wind observations used in, among others, oceanography, numerical weather prediction (NWP) and nowcasting. The purpose of this paper is to review the findings of the SCATSAT-1 CalVal team regarding the stability and performance of version 1.1.3 of the SCATSAT-1 data. The international CalVal team organized by ISRO included participants from various institutions in India, ISRO's Space Applications Centre, KNMI from the Netherlands, and from the USA, NOAA, and NASA's JPL. To perform the evaluation, different centres processed the data independently using heritage processors and made comparisons against NASA's Ku-band QuikSCAT mission, in situ data, and NWP models. We also provide a preliminary assessment of the impact of the SCATSAT-1 data on operational forecasts in India and Europe. We conclude that the SCATSAT-1 data shows significantly improved performance relative to ISRO's OSCAT-1 on Oceansat-2, and that the instrument seems to be stable, given the limited period of observation. The CalVal team has also identified features in the data that could benefit from calibration and processing changes, potentially leading to further improvements on data quality. [ABSTRACT FROM AUTHOR]

The study presents assessment and potential oceanographic applications of sea-surface temperature (SST), ocean net shortwave radiation (SWR) and chlorophyll concentration (CC) observations obtained from various geostationary platforms. SST and SWR from imager on-board Indian National Satellite (INSAT-3D) and CC from Global Ocean Color Imager (GOCI) on-board communication ocean and meteorological satellite (COMS) have been used in the analysis. Relative advantages of high temporal resolution obtained from the geostationary platform compared to polar orbiting platforms are demonstrated. Comparison of INSAT-3D SST with observations gives a correlation of 0.85 and RMSE of 0.81 K. These platforms definitely provide a highly reliable source of continuous observations, which is useful in monitoring dynamic oceanic features such as thermal fronts, chlorophyll blooms, air-sea exchange fluxes, etc. on diurnal to daily timescales. [ABSTRACT FROM AUTHOR]

The first phase of an airborne science campaign has been carried out with the Airborne Visible/Infrared Imaging Spectrometer Next Generation (AVIRIS-NG) imaging spectrometer over 22,840 sq. km across 57 sites in India during 84 days from 16 December 2015 to 6 March 2016. This campaign was organized under the Indian Space Research Organisation (ISRO) and National Aeronautics and Space Administration (NASA) joint initiative for HYperSpectral Imaging (HYSI) programme. To support the campaign, synchronous field campaigns and ground measurements were also carried out over these sites spanning themes related to crop, soil, forest, geology, coastal, ocean, river water, snow, urban, etc. AVIRIS-NG measures the spectral range from 380 to 2510 nm at 5 nm sampling with a ground sampling distance ranging from 4 to 8 m and flight altitude of 4-8 km. On-board and ground-based calibration and processing were carried out to generate level 0 (L0) and level 1 (L1) products respectively. An atmospheric correction scheme has been developed to convert the measured radiances to surface reflectance (level 2). These spectroscopic signatures are intended to discriminate surface types and retrieve physical and compositional parameters for the study of terrestrial, aquatic and atmospheric properties. The results from this campaign will support a range of objectives, including demonstration of advanced applications for societal benefits, validation of models/techniques, development of state-of-the-art spectral libraries, testing and refinement of automated tools for users, and definition of requirements for future space-based missions that can provide this class of measurements routinely for a range of important applications. [ABSTRACT FROM AUTHOR]

Imaging radars provide information that is fundamentally different from sensors that operate in the visible and infrared portions of the electromagnetic spectrum. The Indian Space Research Organisation (ISRO) has launched a multi-mode, multi-polarization Synthetic Aperture Radar (SAR) on-board Radar Imaging SATellite-1 (RISAT-1) on 26 April 2012. Various data products from RISAT-1 SAR are now going through calibration-validation (cal-val) phase and soon will be available for the global users for operational and research purposes. In this regard, algorithms are being developed to retrieve various parameters in diverse application areas. This article deals with the in-house algorithm development for studying different resources using initial available data of RISAT-1. [ABSTRACT FROM AUTHOR]