A. S. Kiran Kumar

Terrain mapping camera for Chandrayaan-1

The Terrain Mapping Camera (TMC) on India’s first satellite for lunar exploration, Chandrayaan-1, is for generating high-resolution 3-dimensional maps of the Moon. With this instrument, a complete topographic map of the Moon with 5 m spatial resolution and 10-bit quantization will be available for scientific studies. The TMC will image within the panchromatic spectral band of 0.4 to 0.9 Μm with a stereo view in the fore, nadir and aft directions of the spacecraft movement and have a B/H ratio of 1. The swath coverage will be 20 km. The camera is configured for imaging in the push broom-mode with three linear detectors in the image plane. The camera will have four gain settings to cover the varying illumination conditions of the Moon. Additionally, a provision of imaging with reduced resolution, for improving Signal-to-Noise Ratio (SNR) in polar regions, which have poor illumination conditions throughout, has been made. SNR of better than 100 is expected in the ±60° latitude region for mature mare soil, which is one of the darkest regions on the lunar surface. This paper presents a brief description of the TMC instrument.

Cross Calibration of the OceanSAT -2 Scatterometer With QuikSCAT Scatterometer Using Natural Terrestrial Targets

The accuracy of ocean surface wind vectors measured by satellite-borne scatterometers depends on measured backscattering coefficient (σ^°). Hence, an in-flight calibration of a satellite scatterometer is essential as this is not guaranteed by its prelaunch absolute calibration. The postlaunch calibration of σ^° is also required to monitor the time evolution of the accuracy of measured σ ^°. This is performed using relative calibration over land targets with minor spatiotemporal variation of σ^°. A few such targets are the Amazon rainforest, Greenland, Antarctica, etc. In this paper, relative calibration of σ^° from the OceanSAT-2 Scatterometer (OSCAT) has been carried out by comparing it with a similar quantity from the Quick Scatterometer (QuikSCAT) for November 2009. The differences between the average σ^° of QuikSCAT and that of OSCAT have been calculated globally to check the overall consistency. Over the calibration sites, the differences are within ±0.25 dB. Histograms of differences in ascending/descending passes and fore/aft looks of OSCAT have also been analyzed over the calibration sites. These indicate that look bias in OSCAT σ^° is within the range of ±0.5 dB. It is also evident that pass biases, i.e., differences between ascending and descending passes, exist over the Amazon rainforest for both QuikSCAT and OSCAT. This diurnal variation in σ^° may go up to 1.25 dB in OSCAT. Further, computations of daily average and standard deviation over the calibration site show that mean OSCAT σ^° is consistent with mean QuikSCAT σ^°, whereas the standard deviation in OSCAT is marginally higher. Further, time-series analysis of OSCAT σ^° shows its temporal stability.

Recent shallow moonquake and impact‐triggered boulder falls on the Moon: New insights from the Schrödinger basin

Shallow moonquakes are thought to be of tectonic origin. However, the geologic structures responsible for these moonquakes are unknown. Here we report sites where moonquakes possibly occurred along young lobate scarps in the Schrodinger basin. Our analysis of Lunar Reconnaissance Orbiter and Chandrayaan-1 images revealed four lobate scarps in different parts of the Schrodinger basin. The scarps crosscut small fresh impact craters ( 1500 boulders associated with trails and bouncing marks. Their origins are largely controlled by recent impact events. Ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed Schrodinger and triggered significant boulder falls about 17 Ma. Therefore, a combination of recent shallow moonquakes and impact events triggered the boulder falls in the Schrodinger basin.

Design of High-Precision ROIC for Quantum Dot Infrared Photodetector

Read out integrated circuit (ROIC) design for quantum dot infrared photodetector (QDIP) array requires large charge handling capacity, low readout noise, minimum detector bias voltage variations, and minimum power dissipation. ROIC design for such applications is challenging due to complex requirements and often needs iterative fabrications to meet all requirements. In this letter, we propose a decision matrixbased optimization method for large dynamic range ROIC implementation. The optimization method is based on trade off analysis, design, and simulation of identified ROIC parameters. This methodology has been applied to an actual case, and the optimum ROIC topology was selected using the optimization method described in this letter. The critical specifications are charge handling capacity of greater than 5 Me and low readout noise of less than 600 electrons, in 180-nm CMOS process. The large dynamic range ROIC consists of a charge integration stage, charge to voltage converters, correlated double samplers, sample and holds, column amplifiers, analog multiplexer, and a buffer amplifier stage. This letter also highlights the measured test chip results of an ROIC array of 30 μm × 30 μm pixel size, in which we have been able to achieve a charge handling capacity of 9.8 Me and the noise of 350 electrons.

Hyper-Spectral Imager in visible and near-infrared band for lunar compositional mapping

India’s first lunar mission, Chandrayaan-1, will have a Hyper-Spectral Imager in the visible and near-infrared spectral bands along with other instruments. The instrument will enable mineralogical mapping of the Moon’s crust in a large number of spectral channels. The planned Hyper-Spectral Imager will be the first instrument to map the lunar surface with the capability of resolving the spectral region, 0.4 to 0.92 Μm, in 64 continuous bands with a resolution of better than 15 nm and a spatial resolution of 80 m. Spectral separation will be done using a wedge filter and the image will be mapped onto an area detector. The detector output will be processed in the front-end processor to generate the 64-band data with 12-bit quantization. This paper gives a description of the Hyper-Spectral Imager instrument.

Iterative method of baffle design for modified Ritchey–Chretien telescope

We developed a baffle design method based on a combination of the results of optical design software and analytical relations formulated herein. The method finds the exact solution for baffle parameters of a modified Ritchey-Chretien telescope by iteratively solving the analytical relations using the actual ray coordinates of the telescope computed with the aid of optical design software. The baffle system so designed not only blocks the direct rays of stray light reaching the image plane but also provides minimum obscuration to imaging light. Based on the iterative method, we proposed a baffle design approach for a rectangular-image-format telescope.

Remote Sensing Data Acquisition, Platforms and Sensor Requirements

AbstractAlthough data available from various earth observation systems have been routinely used in many resource applications, however there have been gaps, and data needs of applications at different levels of details have not been met. There is a growing demand for availability of data at higher repetivity, at higher spatial resolution, in more and narrower spectral bands etc.Some of the thrust areas of applications particularly in the Indian context are;-Management of natural resources to ensure sustainable increase in agricultural production,-Study the state of the environment, its monitoring and assessment of the impact of. various development actions on the environment,-Updating and generation of large scale topographical maps.-Exploration/exploitation of marine and mineral resources and-Operational meteorology and studying various land and oceanic processes to understand/predict global climate changes. Each of these thrust area of application has many components, related to basic resource areas such as agriculture, forestry, water resources, minerals, marine resources etc. and the field of cartography. Observational requirements for major applications have been summarized as under.Monitoring vegetation health from space remains the most important observational parameter with applications, in agriculture, forestry, environment, hydrology etc. Vegetation extent, quantity and temporal changes are the three main requirements which are not fully realized with RS data available. Vegetation productivity, forest biomass, canopy moisture status, canopy biogeochemistry are some examples. Crop production forecasting is an important application area. Remotely sensed data has been used for identification of crops and their acreage estimation. Fragmented holdings, large spread in crop calendars and different management practices continue to pose a challenge lo remote sensing. Remotely sensed data at much higher spatial resolution than hitherto available as well as at greater repetivity are required to meet this need. Non-availability of cloud-free data in the kharif season is one of the serious problems in operational use of remote sensing for crop inventory. Synthetic aperture radar data al X & Ku bands is necessary to meet this demand. Nutrient stress/disease detection requires observations in narrow spectral bands. In case of forestry applications, multispectral data at high spatial resolution of the order of 5 to 10 metres is required to make working plans at forest compartment level. Observations from space for deriving tree height are required for volume estimation. Observations in the middle infrared region would greatly enhance capability of satellite remote sensing in forest fire detection. Temporal, spatial and spectral observational requirements in various applications on vegetation viewing are diverse, as they address processes at different spatial and time scales. Hence, it would be worthwhile to address this issue in three broad categories.a) Full coverage, moderate spatial resolution with high repetivity (drought, large scale deforestation, forest phenology....).b) Full coverage, moderate to high spatial resolution and high repetivity (crop forecasting, vegetation productivity).c) Selected viewing at high spatial resolution, moderate to high repetivity and with new dimensions to imaging (narrow spectral bands, different viewing angles).A host of agrometeorological parameters are needed to be measured from space for their effective use in development of yield models. Estimation of root-zone soil moisture is an important area requiring radar measurements from space. Surface meteorological observations from space at the desired spatial and temporal distributions has not developed because of heavy demands placed on the sensor as well as analytical operational models. Agrometeorology not only provides quantitative inputs to other applications such as crop forecasting, hydrological models but also could be used for farmer advisory services by local bodies.Mineral exploration requires information on geological structures, geomorphology and lithology. Surface manifestation over localized regions requires large scale mapping while the lithology can be deciphered from specific narrow bands in visible. NIR, MIR and TIR regions. Sensors identified for mapping/cartography in conjunction with imaging spectrometer would seem to cover requirements of this application. Narrow spectral bands in the short regions which provide diagnostics of relevant geological phenomenon are necessary for mineral exploration. Thermal inertia measurements help in better discrimination of different rock units. Measurements from synthetic aperture data which would provide information on geological structures and geomorphology are necessary for mineral exploration.The applications related to marine environment fall in three major areas: (i) Ocean colour and productivity, biological resources; (ii) Land-ocean interface, this includes coastal landforms, bathymetry, littoral transport processes, etc. and; (iii) Physical oceanography, sea surface temperature, winds, wave spectra, energy and mass exchange between atmosphere and ocean. Measurement of chlorophyll concentration accurately on daily basis, sea surface temperature with an accuracy of 0.5 °K. and information on current patterns arc required for developing better fishery forecast models. Improved spatial resolution data are desirable for studying sediment and other coastal processes.Cartography is another important application area. The major problems encountered in relation to topographic map updation are location and geometric accuracy and information content. Two most important requirements for such an application are high spatial resolution data of 1 to 2 metre and stereo capability to provide vertical resolution of 1 metre. This requirement places stringent demands on the sensor specifications, geometric processing, platform stability and automated digital cartography.The requirements for the future earth observation systems based on different application needs can be summarized as follows:•Moderate spatial resolution (l50-300m), high repetivity (2 Days), minimum set of spectral bands (VIS, NIR, MIR. TIR) full coverage.•Moderate to high spatial resolution (20-40m), high repetivity (4-6 Days), spectral bands (VIS, MR, MIR, TIR) full coverage.•High spatial resolution (5-10m) muitispectral data with provision for selecting specific narrow bands (VIS, N1R. MIR), viewing from different angles.•Synthetic aperture radar operating in at least two frequencies (C, X, Ku), two incidence angles/polarizations, moderate to high spatial resolution (20-40m), high repetivity (4-6 Days).•Very high spatial resolution (1-2m) data in panchromatic band to provide terrain details at cadastral level (1:10,000).•Stereo capability (1-2m height resolution) to help planning/execution of development plans.•Moderate resolution sensor operating in VIS, NIR, MIR on a geostationary platform for observations at different sun angles necessary for the development of canopy reflectance inversion models.• Diurnal (at least two i.e. pre-dawn and noon) temperature measurements of the earth surface.•Ocean colour monitor with daily coverage.•Multi-frequency microwave radiometer, scatterometer. altimeter, atmospheric sounder, etc.

Land Surface Temperature from INSAT‐3D Imager Data: Retrieval and Assimilation in NWP Model

A new algorithm is developed for retrieving the land surface temperature (LST) from the imager radiance observations on board geostationary operational Indian National Satellite (INSAT-3D). The algorithm is developed using the two thermal infrared channels (TIR1 10.3–11.3 µm and TIR2 11.5–12.5 µm) via genetic algorithm (GA). The transfer function that relates LST and thermal radiances is developed using radiative transfer model simulated database. The developed algorithm has been applied on the INSAT-3D observed radiances, and LST retrieved from the developed algorithm has been validated with Moderate Resolution Imaging Spectroradiometer land surface temperature (LST) product. The developed algorithm demonstrates a good accuracy, without significant bias and standard deviations of 1.78 K and 1.41 K during daytime and nighttime, respectively. The newly proposed algorithm performs better than the operational algorithm used for LST retrieval from INSAT-3D satellite. Further, a set of data assimilation experiments is conducted with the Weather Research and Forecasting (WRF) model to assess the impact of INSAT-3D LST on model forecast skill over the Indian region. The assimilation experiments demonstrated a positive impact of the assimilated INSAT-3D LST, particularly on the lower tropospheric temperature and moisture forecasts. The temperature and moisture forecast errors are reduced (as large as 8–10%) with the assimilation of INSAT-3D LST, when compared to forecasts that were obtained without the assimilation of INSAT-3D LST. Results of the additional experiments of comparative performance of two LST products, retrieved from operational and newly proposed algorithms, indicate that the impact of INSAT-3D LST retrieved using newly proposed algorithm is significantly larger compared to the impact of INSAT-3D LST retrieved using operational algorithm.

Focal length measurement of microlens array for Shack–Hartmann wavefront sensor using interferometer

Abstract. We have proposed a method to determine the focal length of microlens array (MLA) based on the measurement of transverse displacement of image spot in the focal plane for a change of angle of incidence of plane wavefront. An existing interferometer test setup, meant for the surface figure measurement of MLA substrate, along with a charge-coupled device (CCD) is used for this purpose. The interferometer generates as well as measures the angle of incidence of plane wavefront at the MLA, and the transverse displacement of the image spot is determined from images recorded with the CCD. We have also discussed the theory of estimation of the focal length of MLA with spherical wavefront. Error analysis is carried out for both methods and is compared. The proposed plane wavefront method is experimentally demonstrated with an off-the-shelf MLA, and the measured focal length is within 1% of catalogue value.

Design and development of Shack–Hartmann wavefront sensor-based testing of high-resolution optical system for earth observation

Abstract. The deformation of the optical surfaces of a large aperture high-resolution space-borne optical system induced by earth’s gravity on the ground, which is not present during in-orbit operations, necessitates the evaluation of its performance in terms of wavefront error at various stages of development of the earth observation system. A direct method of evaluation for an optical system at an integrated electro-optical module based on a Shack–Hartmann wavefront sensor (SH WFS) is proposed. Design and analysis of the wavefront sensor that are tailored to meet the requirements of the high-resolution optical system are described. We show that the procedure followed for the development of the SH WFS not only addresses the parameters of the wavefront sensor that are critical to its performance, but also aides in the wavefront sensor alignment and calibration. The performance of the developed SH WFS is demonstrated by testing a simulated telescope which is in situ verified in a test configuration using a standard Fizeau interferometer; a close match of the coefficients of Zernike modes between them is established.