nan Ajai

Extraction and validation of cartosat-1 DEM

CARTOSAT-1 satellite, launched in May, 2005 is a dedicated along track stereo mission providing high quality data for topographic and cartographic applications. The present paper describes the evaluation of the Cartosat-1 stereo data, mainly through the generation and validation of DEM for moderately undulating and hilly areas. Photogrammetric techniques have been used for generation of DEM and Orthoimage for two cases i.e. 1) using RPCs (Rational Polynomial Coefficients) and 2) using RPCs along with ground control points. Root Mean Square Error (RMSE) in elevation values for the moderately undulating (Dehradun) and hilly area (Shimla), are found to be 4.38 and 3.69m respectively.

Estimation of Coastal Bathymetry Using RISAT-1 C-Band Microwave SAR Data

The study of swell wave refraction phenomena using synthetic aperture radar (SAR) data has been found to be very useful in estimating the underwater topography (seabed structure). Near-shore water regions generate a wide range of surface signatures due to rapidly changing underwater depths, which cause waves to refract and finally align parallel to the shoreline. Another significant change, which is observed as gravity waves approach the shoreline, is that their wavelength decreases and, as the energy of the wave is constant in the absence of dissipating forces, amplitude increases. The strong correlation between the change in wavelength and the underlying topography makes it possible to estimate the bathymetry from the measured wavelength. Normally available global bathymetric maps (e.g., ETOPO-1 bathymetry toposheets) are out of date and provide bathymetry at a very coarse resolution. In this letter, swell wave refraction phenomena using Radar Imaging Satellite C-band SAR data over coastal regions of Mumbai have been studied. The wave-tracing technique has been used to derive the wavelength of swell waves in near-shore regions and analyze the wavelength change in order to retrieve underwater topography using dispersion relation with swell wave properties. This SAR-based technique can be used to derive high-resolution bathymetric maps for near-coastal regions. Also, with this technique, temporal variations in the seabed can be measured to infer geological processes.

Satellite derived digital elevation model and terrain parameters — generation, accuracy assessment and validation

Digital Elevation Models (DEMs) and their derivatives are routinely exploited for a wide range of planning and engineering applications such as land reclamation, calculation of cut-and-fill requirements for earth works or to determine other relevant geomorphological landscape parameters. The advent of computer (digital) manipulation of elevation data has opened up great possibilities for studying the geometry of our land surface in relation to physical factors such as climate, vegetation, soils and geology. This paper is concerned with the generation, testing and validation of DEM and its derived terrain parameters viz., contours, drainage pattern etc. using IRS-1C stereo pair over a part of Alwar district, Rajasthan, India. In particular, it reports on the results achieved using indigenously developed stereo - processing software along with standard GIS and terrain analysis package to derive DEM and associated terrain parameters of the study area. The results are encouraging when compared with Survey of India topographical maps at 1:50,000 scale in terms of point to point accuracy of DEM, data quality evaluation of orthoimage and higher order drainage delineation.

Bias corrections of CartoDEM using ICESat-GLAS data in hilly regions

There are a number of digital elevation models (DEMs) existing worldwide for studying the topography, estimating elevation differences over time and runoff modeling, soil erosion estimation, and so forth, including vertical changes on glaciers. There are various techniques and instruments/sensors used for surface elevation data collection and for monitoring surface changes. Satellite data-based DEMs have been available at global level during the past two decades. Errors and biases may persist in these elevation data-sets. This may be due to limitations of the techniques, sensor instabilities, bad surveying conditions on the ground, and post-processing artifacts. Elevations derived from Geoscience Laser Altimeter System/Ice, Cloud and land Elevation Satellite (GLAS/ICESat) data are one of the most reliable globally available data. The objective of this study is to present a simple and effective method to compute planimetric offsets in the DEM of hilly terrain using GLAS data and perform necessary corrections for improving the elevation accuracy. A slope-based method has been employed for the co-registration of overlapping elevation surfaces for Chandra and Bhaga basins in the Himalaya. Accuracy assessment has been done by computing standard deviation of offsets, which is an indicator of the variability of error distribution. As a result of bias corrections, the standard deviations have decreased from 10.8 m to 6.0 m and 9.0 m to 7.05 m for Chandra and Bhaga basins, respectively.

Comparative evaluation of various algorithms for drainage extraction using Cartosat-1 stereo data

Hydrological parameters have vital role in civil engineering, infrastructure planning and natural resource management. Since the last one and a half-decade their extraction using the High-resolution satellite stereo data has been very helping and less time consuming. In the earlier times, the ground surveys use to take a lot of time to cover a small area. Whereas with the availability of high accuracy Digital Elevation models from satellite stereo data one can extract these parameters with ease and good accuracy. During last one and half-decade vast experience has been gained in techniques of processing stereo data acquired from space. This paper deals with the extraction and validation of hydrological parameters from digital elevation model (DEM) derived using CARTOSAT-1 stereo data. In this paper two sub-watershed, one in Chamoli, Uttaranchal and other in Shimla, Himachal Pradesh were selected, A detailed morphometric analysis of the derived drainage network from the various sources and using various algorithms has been carried out. The parameters like stream order, stream length, bifurcation ratio, length ratio etc., have been used for comparison purpose.

Absorption characteristics of ocean water in the Arabian Sea during winter bloom from in situ measurements and Oceansat 2 OCM and MODIS data

In the northern Arabian Sea, blooms usually occur during the northeast monsoon (November–January) and inter-monsoon (February–April) periods. After death, these phytoplankton blooms produce massive subsurface zones of low dissolved oxygen levels that have a major impact on the ocean water ecosystem. Many studies have been done to identify the bloom in this region, but those on the optical properties of bloom water are scarce. The present study emphasizes the optical properties (inherent) of the bloom water in the study region using in situ and satellite data. The total absorption coefficient of ocean water was measured from in situ radiance data collected in the northern Arabian Sea from the Sagar Sampada cruise (SS-286) during March 2011. The same data were also derived from the top-of-atmosphere radiance and remote sensing reflectance of the Oceansat 2 Ocean Colour Monitor (OCM-2) and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, respectively. A comparison between measured (in situ) and retrieved total absorption coefficients from OCM-2 was made. The measured and retrieved absorption coefficients are in good agreement. Root mean square errors between measured and retrieved absorption coefficients are 0.018 m−1, 0.026 m−1, and 0.034 m−1 for 490 nm, 510 nm, and 555 nm, respectively. An inter-comparison of total absorption properties retrieved from OCM-2 and MODIS data in the region of one degree radius around the stations was also made. A fairly good match was observed on 10, 14, and 16 March 2011 (coefficient of determination, R2 = 0.75, 0.87, and 0.62, respectively) for the blue band (490 nm) and (R2 = 0.77, 0.79, and 0.71, respectively) the green band (555 nm). The study demonstrates the potential of using remote-sensing optical data for identifying bloom waters.

Morphometric and rheological study of lunar domes of Marius Hills volcanic complex region using Chandrayaan-1 and recent datasets

Marius Hills volcanic complex is one of the most important regions on the lunar surface having an abundant number of volcanic features like domes and cones. Systematic mapping of 106 domes/cones in the Marius Hills region was carried out in this study using high-resolution orthoimage and digital elevation models of Chandrayaan-1 and Kaguya missions. Various morphometric parameters like diameter, height, volume, flank slope, circularity index and form factor are derived for all the mapped domes. The rheological parameters, such as viscosity and eruption rate are estimated for isolated domes and cones superimposed over low domes. The morphometric and rheological properties of these domes are comparable to those located in the area near to Hortensius crater and other mare regions. Surface ages derived for a selected region in NW portion of the Marius Hills volcanic complex using crater size-frequency distribution technique yields ages of 2.98 and 1.91 Ga. It suggests that the domes in this region formed at about 2.98 Ga ago, and then, the younger mare basalts likely embayed this region about 1.98 Ga ago. Stratigraphic sequence of rilles, wrinkle ridge and domes shows that wrinkle ridges are the oldest, while the rilles are younger than the domes.

Models for wheat yield prediction using remotely sensed canopy temperature based indices

Canopy temperature in differentially irrigated and fertilized wheat plots were collected by hand held infrared thermometer from seedling emergence to maturity for two growing seasons (1981–82 and 1982–83). Canopy temperature indices like stress degree day (SDD) and crop water stress index (CWSI) based four-parameter (crop growth stage partitioned) and two-parameter (Non-partitioned) yield models suitable for remote sensing application were developed and tested with observed yield data. From statistical analysis of the models it was concluded that crop growth stage partitioned CWSI or SDD yield model was better than non-partitioned SDD models for predicting wheat grain as well as biological yields.

Remotely sensed canopy temperature based evapotranspiration models for wheat

Field studies were conducted on differentially irrigated wheat (Cv. ‘Sonalika’), on a sandy loam soil at Indian Agricultural Research Institute, New Delhi to evaluate the surface energy balance evapotranspiration (ET) models which use remotely sensed canopy temperature as an input. Four energy balance ET models were used in this study viz. Jackson et. al. (1977) approach; Bartholic et. al. (1970) and stability corrected and uncorrected aerodynamic resistance forms of models. To test the model, ET was estimated using remotely sensed canopy temperatrue, with the remaining to ET measured by water depletion method. Aerodynamic resistance forms of ET models performed well as compared to other models. Results indicate that remotely sensed canopy temperature as an input to surface energy balance models, offers a potential method of estimating ET from a cropped surface.