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The regional coverage satellite constellations are in demand for fulfilling earth observation needs of specific user regions of interest as opposed to global coverage thus enhancing the revisit period for the area. In this paper, we present a few key mission aspects of the regional coverage constellation designed and operated by the Indian Space Research Organization (ISRO) in low earth orbit. ISRO developed three X-Band Synthetic Aperture Radar (SAR) Earth Observation satellites and placed them in three inclined orbit planes to enhance the Indian region's coverage. This is India's first inclined orbit constellation designed for remote sensing applications in low earth orbit. The satellites were built around a standard bus carrying a Synthetic Aperture Radar payload with a deployable Radial Rib Antenna (RRA). They were designed to achieve a high agility capability. As SAR sensors are capable of all-weather, day, and night imaging; thus, most suitable in inclined orbits where the illumination conditions vary continuously for imaging. Though the inclined orbits provide more revisit opportunities to the region of interest, their characteristics pose challenges in mission design and operations. Though the mission design and planning involved a host of elements, this paper brings out the details of a few key mission analysis elements, planning aspects and operations that were critical in the course of various mission phases. The mission analysis included mission-specific requirements like launch windows selection for the constellation and reference attitude generation specific to inclined orbit geometry. Mission planning had to take care of Radial Rib Antenna (RRA) deployment requirements which were very critical for the mission, apart from taking care of individual subsystem requirements. The SAR payload data product quality and targeting accuracy are very sensitive to the satellite image point range (vis-a-vis SAR operation data window). Extensive post-launch calibration activity was carried out to meet all these mission requirements and data product specifications. The challenge was in fixing the payload beam alignment and fixing the uncertainties in onboard and ground computations. The paper also describes the methods of fixing all possible error sources affecting the high-resolution SAR payload performance. • The regional coverage satellite constellations are in demand for area targets coverage. • Inclined orbit constellations are more suitable for regional coverage using SAR sensors. • Mission operations plans need to consider all the specific requirements of spacecraft systems. • Pre-launch and post -launch calibrations of sensors is mandatory for achieving system performance. [ABSTRACT FROM AUTHOR]

Rainfall-induced landslides on steep slopes are potential hazards to life and property. The state of Kerala in India is witnessing unprecedented death and damage since last 3 years due to landslides triggered by heavy rainfall. In this paper, we present a cause-impact analysis of landslides that occurred due to the monsoon rainfall in the years 2018, 2019 and 2020. We have created an event-based landslide inventory post-rainfall season for the entire state and then selected six major landslides for detailed analysis. Event-based landslide inventory maps are prepared from Earth observation satellite data such as Resourcesat-2, 2A, Cartosat-2S, WorldView-2, Pleiades-1A and 1B, SPOT-6 and 7 and Sentinel-2 acquired before and after the rainfall events. Then, rainfall data were analysed to find out the role of daily and antecedent rainfalls on landslide trigger. Finally, we have carried out numerical debris flow modeling to characterise landslides and assess the impact. Our results show that landslides are triggered by antecedent rainfall of variable durations and are mostly debris flow type that has followed the channel path. The runout length and lateral spreads are controlled by variable frictional parameters of the slope material. Furthermore, reactivation at the crown region is also noticed in few cases that need to be monitored. [ABSTRACT FROM AUTHOR]

Abstract: With an array of Indian Remote Sensing Satellites (IRS), a wide variety of national applications have been developed as an inter-agency effort over the past 20 years. Now, the capacity of the programme has been extended into the global arena and IRS is providing operational data services to the global user community. The recently launched IRS satellite, Resourcesat-1, was placed into perfect orbit by India''s PSLV and is providing valuable imaging services. Resourcesat-1 is actually like 3 satellites “rolled” into one, imaging a wide field of 710km area at 55m resolution in multispectral bands from the AWiFS, 23m resolution in a systematic 142km swath from four bands of the LISS-3 and the 5.8m multi-spectral images from the most advanced sensor—LISS-4. Yet another aspect of Resourcesat-1 is it that it marks a “watershed” in terms of a quantum jump in technological capability that India has achieved compared to past missions. The mission has many newer features—the advanced imaging sensors, the more precise attitude and orbit determination systems, the satellite positioning system onboard, the mass storage devices and many other features. This mission has led IRS into a new technological era, and when combined with the technological capability of the forthcoming Cartosat missions, India would have developed technologies that will take us into the new generation of EO satellites for the coming years. This paper provides a detailed description of the Resourcesat-1 mission. From the applications point of view, Resourcesat-1 will open up new avenues for environmental monitoring and resources management—especially for vegetation assessment and disaster management support. The monitoring capability of this mission is also extremely important for a number of applications. The mission has global imaging and servicing capabilities and could be received through the Antrix-Space Imaging network, which markets Resourcesat-1 data worldwide. This paper also describes the applications potentials and global capabilities of the mission. Resourcesat-1 will have continuity and after that a new generation system will provide enhanced and more unique imaging services. Actually, India has a 25 years strategy for EO and a perspective of the same is also described in this paper. [Copyright &y& Elsevier]

This paper covers different aspects related to X-ray fluorescence activities at Saha Institute of Nuclear Physics, Kolkata, India. In its first part, experiments on basic physical problems are illustrated and in the second part, some applications related to X-ray fluorescence are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The mission of the COMPASS-1 picosatellite is to take pictures of the earth, to validate a space-borne GPS receiver developed by the German Aerospace Center, and to verify the proper operation of the magnetic attitude control system in orbit. The spacecraft was launched on April 28, 2008 from the Indian space port Sriharikota, as part of the PSLV-C9 world record launch that simultaneously brought ten satellites into orbit. The mission operations were carried out from the ground stations in Aachen and Tainan. Arising difficulties in the communication link were overcome with the support of individuals from the amateur radio community. After several months of mission operation, abundant housekeeping and mission data has been commanded, received and analyzed and is presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the impact of extensive anthropogenic activities associated with festivities and agricultural crop residues burning in the Indo-Gangetic Plains (IGP) on satellite-derived reflectance during November 2007. Intense smoke plumes were observed in the IRS-P4 OCM satellite data over IGP associated with agricultural crop residue burning during the study period. Terra-MODIS AOD and CALIPSO LIDAR backscatter datasets were analysed over the region to understand the spatial and temporal variation of the aerosol properties. Ground-based measurements on aerosol optical properties and black carbon (BC) mass concentration were carried out during 7–14 November 2007 over urban region of Hyderabad, India. Top of the Atmosphere (TOA) reflectance estimated from IRS-P4 Ocean Color Monitor (OCM) data showed large variations due to anthropogenic activities associated with crop residue burning and fireworks. Atmospheric corrections to OCM satellite data using 6S radiative transfer code with inputs from ground and satellite measurements could account for the variations due to differential aerosol loading. Results are discussed in this paper. [Copyright &y& Elsevier]

Space research in India began in the early sixties, with the establishment of the Thumba Equatorial Rocket Launching Station. Indigenously developed rocket payloads were carried in foreign rockets and flown for studying various atmospheric parameters, which are unique to the tropics. In the seventies, Indian-made rockets became available. Since then, there has been rapid progress in the technical advancement, which helped the atmospheric scientists in taking up more challenging and contemporary problems, related to mesospheric winds, ionospheric irregularities, stratospheric ozone, role of aerosols in atmospheric radiative transfer, etc. India entered into the satellite era in 1975, with the development of the Aryabhatta satellite, the first Indian experimental satellite, followed by Bhaskara-1 in 1979, which carried a microwave radio meter for retrieval of atmospheric water vapour and cloud liquid water contents. Since then, there have been several satellites, such as the INSAT series for meteorology and communication, Indian Remote Sensing (IRS) satellite series, and Stretched Rohini Satellite System (SROSS) for in situ observation of the ionosphere, which are all built in India and launched from Indian soil. High quality data being obtained from these satellite missions are helping scientists in taking up problems that are of regional and global scales and in studying the changes that are taking place in the earth atmosphere system, in a more holistic way. This paper attempts to provide an overview of the scientific developments and highlights some results. [ABSTRACT FROM AUTHOR]

This paper presents a summary of the efforts at ISRO for the development of spacecraft technology over the past three decades and also outlines technological trends for the evolution of communication space platforms, as well as scientific and remote sensing satellite systems. Tracing the developmental efforts since Aryabhatta, the first Indian satellite, through the experimental phase of application-oriented remote sensing and communication satellites namely Bhaskara-I, Bhaskara-II and Apple, the state-of-art operational INSAT and IRS series of satellites are presented. The communication satellite platforms namely I-1K, I-2K, I-3K and I-4K with lift off masses in the range of one to four tonnes, power generation capabilities of 1 kW to 10 kW and more, meeting multifarious requirements of telecommunication, telecasting, DTH (Direct to Home TV) multimedia applications and meteorological services have been developed. The improvements derived from the usage of multijunction solar cells, lithium-ion batteries and other mass optimization techniques are passed on for larger payload compliment and longer life. Technological trends in the design of communication payloads and the advancements in key elements such as antennas, microwave power amplifiers and receive systems as well as spacecraft mainframe are discussed. Commercialization of developmental efforts in the form of design, building and commissioning of communication satellites for the international service providers are highlighted in brief. [ABSTRACT FROM AUTHOR]

On the Indian subcontinent, scintillations are quite frequent and intense and have a longer duration during a peak period of an 11-year solar cycle. This phenomenon quite significantly informs us about the performance of the Global Positioning System (GPS). A special experiment has particularly been conducted to study the effect of scintillations on GPS time. This paper discusses the findings of this experiment. A degradation of timing accuracy of the order of 60 ns has been observed. [ABSTRACT FROM AUTHOR]

This paper reports results on the LAI Retrieval and Validation Experiment (LRVE) that was conducted for two agricultural areas in Central India during the winter season of 2001–2002. The study aimed at relating field measurements of leaf area index (LAI) to spaceborne Indian Remote Sensing Satellite (IRS) Linear Imaging Self Scanning Sensor-III (LISS-III) data, preparation of site-level LAI maps, and validation of Moderate Resolution Imaging Spectroradiometer (MODIS) 1-km LAI global fields. Measurements of field-level LAI, aerosol optical thickness and water vapor were carried out on the day of LISS-III overpasses. Empirical models based on the site-specific LAI-vegetation index relation were developed and used to generate 23-m resolution LAI maps for two sites (Indore and Bhopal) covering 30 km × 30 km. These LAI images were degraded to 1-km spatial resolution and used for validation of the version 3 and 4 MODIS LAI products (MOD15A2). The results indicate a positive correlation (r = 0.78) between LAI derived from LISS-III data and MODIS data. However an overestimate by a factor of 1.6 to 2.5 in the version 3 MODIS product is observed with root mean square error (RMSE) ranging from 0.20 to 1.26. The factor of overestimation reduces significantly by 50% and RMSE by 40% when version 4 MODIS LAI was analyzed. The improvement in accuracy was observed to be associated with the change in algorithm path adopted for retrieving version 3 and 4 MODIS LAI. Analysis of the MODIS land cover product that is an input in the MODIS LAI retrieval algorithm indicated errors in assigning land cover classes for the study sites, which could be one of the sources of error in MODIS LAI product. [ABSTRACT FROM AUTHOR]

In this paper, methods for the generation of residual and prospecting geoids and free-air gravity anomaly using satellite altimeter data are developed. Maps of residual geoid, gravity anomaly, and their spectral components generated over Indian offshore using ERS-1 altimeter data are presented and interpreted. A number of known megastructures over the study area, for example, Bombay High, Saurastra platform, 90 east ridge, etc., are interpreted successfully from these maps. Some of the anomalous zones (the basins near Mangalore and off Bombay High in the western offshore and Palar basin off Madras coast in the eastern offshore) have been identified as potential sites for occurrences of hydrocarbon-bearing structures, for which detailed ship-borne geophysical surveys have been commissioned by the Oil & Natural Gas Corporation (ONGC), Dehradun, India. [ABSTRACT FROM AUTHOR]