High Resolution Visible Images Research Articles

Ice-flow features on Ice Stream B, Antarctica, revealed by SPOT HRV imagery

AbstractNumerous features of glaciological significance appear on two adjoining SPOT High Resolution Visible (HRV) images that cover the onset region of Ice Stream B, Antarctica. Many small-scale features, such as crevasses and drift plumes, have been observed in aerial photography. Subtle large-scale features, such as long flow traces that have not been mapped previously, are clear in the satellite imagery. Newly discovered features include ladder-like runners and rungs within certain shear margins, flow traces that are parallel to ice flow, unusual crevasse patterns and flow traces originating within shear margins.

Ice-flow features on Ice Stream B, Antarctica, revealed by SPOT HRV imagery

AbstractNumerous features of glaciological significance appear on two adjoining SPOT High Resolution Visible (HRV) images that cover the onset region of Ice Stream B, Antarctica. Many small-scale features, such as crevasses and drift plumes, have been observed in aerial photography. Subtle large-scale features, such as long flow traces that have not been mapped previously, are clear in the satellite imagery. Newly discovered features include ladder-like runners and rungs within certain shear margins, flow traces that are parallel to ice flow, unusual crevasse patterns and flow traces originating within shear margins.

A preliminary comparison of Landsat Thematic Mapper and SPOT-l HRV multispectral data for estimating coniferous forest volume

Digital Landsat Thematic Mapper (TM) and SPOT high-resolution visible (HRV) images of coniferous forest canopies were compared in their relationship to forest wood volume using correlation and regression analyses. Significant inverse relationships were found between softwood volume and the spectral bands from both sensors (P less than 0.01). The highest correlations were between the log of softwood volume and the near-infrared bands.

Estimating biomass of an improved pasture using SPOT HRV data

AbstractSPOT high‐resolution visible (HRV) multispectral data were used to estimate the biomass of an improved pasture near Clare in South Australia. The study examined the effects of trees, senescent vegetation, surface wetness, herbage composition and management practices including the age of the pasture and stocking rate, on reflectance. This was undertaken by a comparison of spectral responses and through the use of partial correlation analyses. Changes in biomass had the greatest influence on reflectance, though the presence of trees and senescent vegetation influenced reflectance significantly in all wavebands. These areas were excluded from the model developed to estimate pasture biomass. The regression model was inverted and applied to a normalized difference SPOT HRV image. The accuracy of the biomass estimation was 43–81% at the 95% confidence level, or ±57.0 gm−2 of dry grass. This technique provides resource managers with a tool for routinely assessing pasture condition over large areas.

Space station negotiations successfully completed

In recent years, there have been many land-surface studies based on visible and near-infrared reflectance values retrieved from the Landsat Thematic Mapper (TM) and SPOT High Resolution Visible (HRV) sensors. Retrieval of reflectance from satellite sensor digital count requires knowledge of the atmospheric conditions and the sensor absolute calibration. In most cases, atmospheric conditions are simulated with a radiative transfer code and sensor calibration coefficients are obtained from preflight sensor calibrations or in-flight calibrations over bright surfaces (such as White Sands, New Mexico, USA, or La Crau, France). Though these procedures are well accepted, there have been few studies specifically designed to validate the accuracy of such reflectance factor retrievals (RFR) for both bright and dark targets. Data from two experiments conducted in an agricultural region in central Arizona were analyzed to quantify the accuracy of RFR from the Landsat TM and SPOT HRV sensors. These data included measurements made with groundbased and aircraft-based four-band radiometers and the NASA Advanced Solid-State Array Spectrometer (ASAS) aboard a C130 aircraft, and TM and HRV images acquired at nadir and off-nadir viewing angles. Results showed that the off-nadir reflectance factors measured using ground- and aircraft-based instruments, including ASAS, were comparable. The RFR from the satellite-based TM and HR V sensors generally resulted in an overestimation of dark target reflectance (up to 0.05 reflectance in the visible) and an underestimation of bright target reflectance (up to 0.1 reflectance in the near-infrared). Even greater error was possible when RFR was based on outdated sensor calibrations, particularly those conducted prelaunch. There was supporting evidence from studies at three sites (White Sands, New Mexico; Maricopa, Arizona; and Walnut Gulch, Arizona) that the Landsat-5 TM sensor sensitivity may have degraded by as much as 20% from the prelaunch calibration. Regarding the potential error in RFR related to recent changes in the processing of Landsat TM data (Level-0 and Level-1) by EOSAT Corporation, we found that the Level-0 data was slightly greater (∼2 digital counts) than the Level-1 data for all bands and all targets in our study.

A high resolution phosphor screen for XUV detectors

The authors describe an XUV detector with a spatial resolution of approximately=6 mu m designed to fly on the normal incidence X-ray telescope (NIXT) rocket package. The telescope is a 10 in (254 mm) diameter Ritchey-Chretien system which relies on unusually high accuracy multilayer coatings to image active regions on the Sun. The coatings are reflective in a narrow band centred on a wavelength near 6.3 nm; thus the detector's jog is to convert the XUV image into an electronic format which can be stored on tape or relayed to the ground via telemetry. The authors are primarily concerned with how the X-rays are converted into a very high resolution visible light image which can be sensed and read out by the image processing electronics.