Indian Earth Observation (EO) Programme, since its inception has been applications driven and national development has been its main motivation. In order to meet the observational requirements of many societal benefit areas, a series of EO systems have been launched in both polar and geo synchronous orbits. Starting from Bhaskara, the first experimental EO satellite in 1979 to Cartosat-1 successfully launched in May 2005, a large number of sensors operating in optical and microwave spectral regions, providing data at resolutions ranging from 1 km to a meter have been built and flown. Data reception and processing facilities have been established not only in the country but also at various international ground stations. Remotely sensed data and its derived information have become an integral component of the National Natural Resources Management System (NNRMS), a unique concept evolved and established in the country. The paper discusses the evolution of IRS satellite systems, application programmes in different societal benefit areas and the road ahead. How it complements and supplements the international efforts in the context of Global Earth Observation System of Systems has also been indicated.

India and the United States of America (U.S.A.) held a joint conference from June 21-25, 2004 in Bangalore, India to strengthen and expand cooperation in the area of space science, applications, and commerce. Following the recommendations in the joint vision statement released at the end of the conference, the National Oceanic and Atmospheric Administration (NOAA) and the Indian Space and Reconnaissance Organization (ISRO) initiated several joint science projects in the area of satellite product development and applications. This is an extraordinary step since it concentrates on improvements in the data and scientific exchange between India and the United States, consistent with a Memorandum of Understanding (MOU) signed by the two nations in 1997. With the relationship between both countries strengthening with President Bush's visit in early 2006 and new program announcements between the two countries, there is a renewed commitment at ISRO and other Indian agencies and at NOAA in the U.S. to fulfill the agreements reached on the joint science projects. The collaboration is underway with several science projects that started in 2005 providing initial results. NOAA and ISRO agreed that the projects must promote scientific understanding of the satellite data and lead to a satellite-based decision support systems for disaster and public health warnings. The projects target the following areas: --supporting a drought monitoring system for India --improving precipitation estimates over India from Kalpana-1 --increasing aerosol optical depth measurements and products over India --developing early indicators of malaria and other vector borne diseases via satellite monitoring of environmental conditions and linking them to predictive models --monitoring sea surface temperature (SST) from INSAT-3D to support improved forecasting of regional storms, monsoon onset and cyclones. The research collaborations and results from these projects will be presented and discussed in the context of India-US cooperation and the Global Earth Observation System of Systems (GEOSS) concept.

The NOAA/NESDIS has been conducting studies to see if user requirements can be met by a single constellation of satellites that would provide high spatial, temporal and spectral resolution data every 15 minutes every where in post GOES-R and NPOESS time frame. The current Geostationary Operational Environmental Satellites (GOES) at an altitude of 35,000 km provide observations up to local zenith angles of 75 degrees for monitoring severe weather in real time. The Polar-orbiting Operational Environmental Satellites (POES) at an altitude of 833 km complement monitoring in the polar region at a regular time interval. The POES and DMSP (Defense Meteorological Satellite Program) satellites will be merged into a new satellite system referred to as the National Polar-orbiting Operational Environmental Satellite System (NPOESS) which is under development. The Jet Propulsion Laboratory (JPL) has been supporting this study by analyzing characteristics of Medium Earth Orbits (MEO) as an observation venue to meet user requirements. An optimal altitude of 10,400 km has been selected based on the manageable radiation impacts on the electronics. This paper presents the initial encouraging results in several areas such as: orbit selection, constellation, coverage, revisit time analyses, communications options, scan mechanisms, and instrument concepts.

ADEOS II was launched on Dec., 2002. However, after about 10 months operation, it has lost most of its power due to the solar paddle failure. As a follow on of ADEOS II mission, JAXA is now planning GCOM mission which is composed of a series of satellites. They are now tentatively called GCOM-W and GCOM-C satellites. Both satellites are composed of 3 satellites with 5 year lifetime. Hence, 13 years of continuous observation can be assured with 1 year overlaps. The first satellite of GCOM-W will be launched in fiscal 2010 while the first one of GCOM-C will be launched in fiscal 2011. GCOM-W will carry AMSR F/O (tentatively called as AMSR2). AMSR2 will be very similar to AMSR on ADEOS II and AMSR-E on EOS-Aqua with some modifications. The orbit of GCOM-W is 700km altitude and 13:30 ascending node time (TBD) to continue the AMSR-E observation. GCOM-C will carry GLI F/O (tentatively called as SGLI). The SGLI will be rather different from GLI. The main targets of SGLI are atmospheric aerosols, coastal zone and land. In order to measure aerosols over both ocean and land, it will have an ultra violet channel, as well as polarization and bi-directional observation capability. For, coastal zone and land observation, the IFOV of SGLI for these targets will be around 250m. The instrument will be composed of several components. The shorter wavelength region will adopt push broom scanners, while long wave region will use a conventional whisk broom scanner. The orbit of GCOM-C is the same to that of ADEOS II, i.e. around 800km altitude, and 10:30 descending node time.

This paper presents the salient features of INSAT 3D mission and its Met Payloads. INSAT-3D, the next ISRO meteorological satellite aims for a significant technological improvement in sensor capabilities as compared to earlier INSAT missions. It is an exclusive mission designed for enhanced meteorological observations and monitoring of land and ocean surfaces for weather forecasting and disaster warning. The three-axis stabilized geostationary satellite is to carry two meteorological instruments: a six channel Imager and an IR Sounder. Along with the channels in Visible, Middle Infrared, Water Vapor and Thermal Infrared bands, the Imager includes a SWIR channel for wider applications. The Sounder will have eighteen narrow spectral channels in three IR bands in addition to a channel in visible band. INSAT-3D is configured around standard 2000 kg I2K spacecraft bus with 7-year life. Several innovative technologies like on-the-fly correction of scan mirror pointing errors, biannual yaw rotation of the spacecraft, micro-stepping SADA, star sensors and integrated bus management unit have been incorporated to meet the stringent payload requirements like pointing accuracies, thermal management of IR detectors and concurrent operation of both instruments.

The Global Precipitation Measurement (GPM) mission is an expanded follow-on mission of the current Tropical Rainfall Measuring Mission (TRMM). The concept of GPM is, 1) TRMM-like, non-sun-synchronous core satellite carrying the Dual-frequency Precipitation Radar (DPR) to be developed by Japan and a microwave radiometer to be developed by United States, and 2) constellation of satellites in polar orbit, each carrying a microwave radiometer provided by international partner. The constellation system of GPM will make it possible every three-hour global precipitation measurement. Because of its concept on focusing high-accurate and high-frequent global precipitation observation, GPM has a unique position among future Earth observation missions. GPM international partnerships will embody concept of GEOSS. Observation data acquired by the GPM mission are expected to be used for both Earth environmental research and various societal benefit areas. One of most expected application fields is weather prediction. Use of high-frequent observation in numerical weather prediction models will improve weather forecasting especially for extreme events such as tropical cyclones and heavy rain. Another example is application to flood monitoring and forecasting. Recent increasing needs of real-time flood information required from many countries especially in Asia will strongly support operational application of GPM products in this field.

Monitoring of the Geo-physical and Bio-geo-physical parameters of the global oceans at meso-scales is an important aspect of the Space borne Earth Remote sensing for weather forecasting and climatic studies. ISRO has initiated action in this direction by launching the IRS-P4 satellite in May 1999 which carried two instruments, an Ocean Colour Monitor (OCM) and a Multi-frequency Scanning Microwave Radiometer (MSMR). These payloads provided valuable data over Indian ocean with limited global coverage for many applications like PFZ, SST, water vapour content, monsoon forecasting etc,. The Oceansat-2 Mission will provide continuity of services of IRS-P4 with enhanced application potential. It will carry a Ku-Band pencil beam Scatterometer for global wind vector measurements and OCM with optimized spectral characteristics. The Satellite is configured to support these Payloads operation covering the global oceans with a two-day repetevity. While meeting the continued demand of its present data users, the OCM will have several enhanced applications in the areas of Chlorophyll concentration and primary productivity, suspended sedimentation dynamics, Carbon cycle monitoring, marine pollutants/oil slicks etc,. The Ku-band Scatterometer will cover ~ 97% of the global oceans daily and will provide measurements of surface wind vectors. This data will be a major input for the local weather forecasting and NWP models. The Scatterometer data is also used for sea state forecasting and ocean dynamics, monitoring of extreme events like cyclones/hurricanes, Polar Ice studies etc,. In this paper, a brief description of the Payload Instruments, Satellite Mainframe elements, Mission operations plan and typical applications are covered.

Increasingly, data from multiple sensors are used to gain a more complete understanding of land surface processes at a variety of scales. The Landsat suite of satellites has collected the longest continuous archive of multispectral data. The ResourceSat-1 Satellite (also called as IRS-P6) was launched into the polar sun-synchronous orbit on Oct 17, 2003. It carries three remote sensing sensors: the High Resolution Linear Imaging Self-Scanner (LISS-IV), Medium Resolution Linear Imaging Self-Scanner (LISS-III), and the Advanced Wide Field Sensor (AWiFS). These three sensors are used together to provide images with different resolution and coverage. To understand the absolute radiometric calibration accuracy of IRS-P6 AWiFS and LISS-III sensors, image pairs from these sensors were compared to the Landsat-5 TM and Landsat-7 ETM+ sensors. The approach involved the calibration of nearly simultaneous surface observations based on image statistics from areas observed simultaneously by the two sensors.

Absolute sensor calibration is the basis on which measured radiance from multiple sensors can be compared with each other or with time. Despite the increasing sophistication and reliability of on-board satellite sensor calibration systems, vicarious (or ground-look) calibration methods remain an important component of calibration validation. These methods, particularly the surface reflectance method, typically involve intensive measurements, at the time of satellite over-flight, of the surface and atmospheric properties (such as, surface reflectance and temperature, atmospheric pressure, water vapor and temperature profiles, and aerosol optical properties) that are ideally uniform, stable, and well defined. Such conditions are found, for example, in the desert southwest of the United States or in the atmosphere above high altitude lakes. A key measurement that has been often neglected and one that is becoming increasingly important due to rapid industrialization of developing countries, is the single scattering albedo of aerosols--a measure of the fraction of light that is scattered from the total amount extinguished from the direct beam; typical values range from close to 1 to 0.8 or lower for highly absorbing aerosols. It is obtained from a measurement of aerosol absorption for which many techniques are available. The error in the measurement of absorptance disproportionately impacts the error in the scattered radiance as seen by the remote sensor. Here we describe the sensitivity of sensor calibration to aerosol absorption and illustrate why it should be an important measurement in the field calibration campaigns, including those planned for the next generation satellites of the US National Polar-Orbiting Operational Environmental Satellite System.

Despite having half a dozen operational EO missions already in the orbit, the need to have dedicated constellation of EO satellites emanates from India's perennial vulnerability to the natural disasters. Capturing an event in real time, along with the appropriate spatial attributes--characterizing the impacts, precursors and other inter-relations, is critically a missing link. Potentially, a dedicated constellation of EO satellite--with suitable mix of optical and SAR payloads captures the events in its real time form. The right choice of sensors holds the key for low cost autonomous missions characterizing the constellation. It is visualized to have AWiFS type of camera with visible, near infrared, short wave infrared and thermal sensors onboard GEO mission. The optical LEO missions could include LISS 3&4 type of cameras along with C band SAR. For 'formation flying', a set of visible/infrared imagers, infrared sounders, microwave imagers, microwave sounders, scatterometers and radar altimeters with suitable bands, data rate and resolutions assumes significance. It has been visualized to make strategic transition of India's planned and future EO missions to a system of thematic constellations, wherein AWiFS could move to GEO; RESOURCESAT and RISAT could converge into a LEO constellation; OCEANSAT would lead transition into 'formation flying'. The paper intends to describe such strategies.

A CCD based characterization setup comprising of a light source, CCD linear array, Electronics for signal conditioning/ amplification, PC interface has been developed to generate images at varying densities and at multiple view angles. This arrangement is used to simulate and evaluate images by Super Resolution technique with multiple overlaps and yaw rotated images at different view angles. This setup also generates images at different densities to analyze the response of the detector port wise separately. The light intensity produced by the source needs to be calibrated for proper imaging by the high sensitive CCD detector over the FOV. One approach is to design a complex integrating sphere arrangement which costs higher for such applications. Another approach is to provide a suitable intensity feed back correction wherein the current through the lamp is controlled in a closed loop arrangement. This method is generally used in the applications where the light source is a point source. The third method is to control the time of exposure inversely to the lamp variations where lamp intensity is not possible to control. In this method, light intensity during the start of each line is sampled and the correction factor is applied for the full line. The fourth method is to provide correction through Look Up Table where the response of all the detectors are normalized through the digital transfer function. The fifth method is to have a light line arrangement where the light through multiple fiber optic cables are derived from a single source and arranged them in line. This is generally applicable and economical for low width cases. In our applications, a new method wherein an inverse multi density filter is designed which provides an effective calibration for the full swath even at low light intensities. The light intensity along the length is measured, an inverse density is computed, a correction filter is generated and implemented in the CCD based Characterization setup. This paper describes certain novel techniques of design and implementation of system calibration for effective Imaging to produce better quality data product especially while handling high resolution data.

SAR Payload of RISAT (Radar Imaging Satellite), the first SAR satellite from ISRO, is currently under development. This payload is based on active antenna technology, and it supports variety of resolution and swath requirements in C-band. Both conventional stripmap and scanSAR modes are supported with dual polarization operation. Additionally a quad polarization stripmap mode is provided for availing additional resource classification. In all these modes resolutions from 3m-50 m can be achieved with swath ranging 30 km -240 km. On experimental basis, a sliding spotlight mode is also available. The payload hardware is organized in such a way that that co and cross polarization images are available for any operating modes. Additionally, a quad polarization mode is also supported. Active array configuration of this payload called for development of many new technologies ranging from MMICS, TR modules, miniaturised power supplies, high speed digitisers, dual polarized printed antenna and distributed control systems. A completely new bus is being designed for aiding the payload operation. The RISAT spacecraft is configured around the payload to minimize the spacecraft weight, suitable for launching by ISRO's PSLV launcher. RISAT will be placed on dawn to dusk sunsynchronous polar orbit to ensure maximum solar power availability. All the basic building blocks have already crossed design stage and have undergone rigorous space qualification program. Presently a complete SAR with one tile has been integrated as design verification model and is under rigorous testing. This development ensured demonstration of end to end hardware, on-board control software and beam control behavior.

The Indian Space Research Organisation (ISRO) has established an operational Remote sensing satellite system by launching its first satellite, IRS-1A in 1988, followed by a series of IRS spacecraft. The IRS-1C/1D satellites with their unique combination of Payloads have taken a lead position in the Global remote sensing scenario. Realising the growing User demands for the "Multi" level approach in terms of Spatial, Spectral, Temporal and Radiometric resolutions, ISRO identified the Resourcesat as a continuity as well as improved RS Satellite. The Resourcesat-1 (IRS-P6) was launched in October 2003 using PSLV launch vehicle and it is in operational service. Resourcesat-2 is its follow-on Mission scheduled for launch in 2008. Each Resourcesat satellite carries three Electro-optical cameras as its payload - LISS-3, LISS-4 and AWIFS. All the three are multi-spectral push-broom scanners with linear array CCDs as Detectors. LISS-3 and AWIFS operate in four identical spectral bands in the VIS-NIR-SWIR range while LISS-4 is a high resolution camera with three spectral bands in VIS-NIR range. In order to meet the stringent requirements of band-to-band registration and platform stability, several improvements have been incorporated in the mainframe Bus configuration like wide field Star trackers, precision Gyroscopes, on-board GPS receiver etc,. The Resourcesat data finds its application in several areas like agricultural crop discrimination and monitoring, crop acreage/yield estimation, precision farming, water resources, forest mapping, Rural infrastructure development, disaster management etc,. to name a few. A brief description of the Payload cameras, spacecraft bus elements and operational modes and few applications are presented.