Shuttle Imaging Radar Research Articles

The Separation of Sea-Ice Types in Radar Imagery (Abstract)

The ability to distinguish the several major types of sea ice with active radar instruments has been well studied in recent years. The separation of sea-ice types by radar results principally from variations in radar back-scatter due to characteristic differences of these ice types in surface morphology and brine content. When sea ice is viewed with an active radar at angles greater than about 20° from nadir, undeformed ice reflects radar waves and results in a low return, while ridges, hummocks, and small-scale surface features scatter the radar waves and produce a high return. The presence of salt increases the dielectric constant of ice; penetration by radar into the ice is then negligible, and the return is essentially determined by surface morphology. The absence of salt reduces the dielectric properties of ice; radar waves can then penetrate the ice to some depth and are scattered by air bubbles and brine-drainage channels (called volume scattering), thereby enhancing the return even for roughened surfaces. All these properties vary significantly with radar frequency and polarization as well as seasonally. For example, higher radar frequencies respond to smaller-scale surface features, while lower radar frequencies penetrate further into the ice with resulting volume scattering. The high-resolution imagery from synthetic aperture radars (SAR), mounted on aircraft, shuttle, or satellite platforms, is very effective for many sea-ice studies, including the separation of ice types. An aircraft-mounted X-band (9 GHz) SAR, for example, can discriminate smooth first-year ice, rough first-year ice, multi-year ice, and open water by the intensity (tone) of the radar returns and floe geometry. The preferred SARs to date for satellites and shuttle platforms have been L-band (1–2 GHz) systems. SAR imagery of sea ice was extensively acquired by Seasat in 1978 over the Beaufort Sea, with limited quantities obtained by the Shuttle Imaging Radar (SIR-B) over the Weddell Sea in 1984. While L-band SAR can discriminate rough and smooth ice along with roughened open water based on image intensity and floe geometry, the returns from thick first-year ice and multi-year ice are not clearly distinguishable. The fact that there is volume scattering from multi-year ice suggests that there may be textural or spatial frequency variations that could be used to separate these two major ice types in radar imagery. In order to investigate the separation of sea-ice types in the large amount of L-band SAR imagery available, image-analysis techniques including filtering and classification programs have been utilized, pointing towards an automatic classification algorithm for use in future SAR sea-ice data sets, especially from space. An important characteristic of all SAR imagery is the presence of image speckle, a coherent form of noise caused by the random variability of scatterers across even a uniform surface. Most SAR processors reduce this effect by averaging multiple independent samples but this is done at the cost of reducing resolution. Speckle reduction can also be accomplished by filtering. Several filters have been tested including median, box, and adaptive edge filters. Each filter has different characteristics in terms of smoothing speckle and in the response to sharp gradients or edges, such as ridge or lead openings, as well as computational requirements. Optimization of each filter’s parameters has been determined by the quality of classification of each ice type. The classification programs that have been tested are based on tone and texture image characteristics. The programs are supervised; that is, a small training area for each class is pre-selected for statistical analysis. From these statistics, the remainder of the imagery is subjected to the particular classification algorithm. The tone program separates classes based on the mean, standard deviation, and number of standard deviations of each class, and includes a Bayesian maximum-likelihood classifier for ambiguous elements. The texture program determines the statistical homogeneity of each class and the optimal segmentation of each small area into the various classes.

Shuttle Imaging Radar (SIR-B) Investigations of the Canadian Shield: Initial Report

Two of the 43 Shuttle Imaging Radar (SIR-B) experiments carried out from the 41-G shuttle mission in 1984 involved a 2600-km swath across the Canadian Shield, with the objectives of studying the structure of province boundaries and developing techniques for the geologic use of orbital radar. Despite degraded single incidence angle imagery resulting from system problems, valuable experience has been obtained with data over a test site near Bancroft, Ontario. It has been found that even subdued glaciated topography can be effectively imaged, variations in backscatter being caused by variations in local incidence angle rather than shadowing. It has been demonstrated that small incidence angles are more sensitive to topography than large angles. Backscatter is extremely sensitive to look direction, topographic features nearly normal to the illumination being highlighted, and those nearly parallel to it being suppressed. It is concluded that orbital radar can provide a valuable tool for geologic studies of the Canadian Shield and similar areas, if suitable look angles and at least two look directions can be utilized for each area.

Preliminary analyses of SIR-B radar data for recent Hawaii lava flows

The Shuttle Imaging Radar (SIR-B) experiment acquired two L-band (23 cm wavelength) radar images (at about 28° and 48° incidence angles) over the Kilauea Volcano area of southeastern Hawaii. Geologic analysis of these data indicates that, although as lava flows and pyroclastic deposits can be discriminated, pahoehoe lava flows are not readily distinguished from surrounding low return materials. Preliminary analysis of data extracted from isolated flows indicates that flow type (i.e., as or pahoehoe) and relative age can be determined from their basic statistics and illumination angle.

Space-borne radar for monsoon and storm induced flood control planning in Bangladesh: A result of the shuttle imaging radar-B program

In October of 1984, the National Aeronautics and Space Administration flew an L-band imaging radar device aboard the Space Shuttle Challenger as part of the Shuttle Imaging Radar (SIR-B) Program. During the mission, radar data were acquired over the Peoples Republic of Bangladesh. With Bangladesh as an example, the data were obtained in an effort to examine the potential of radar remote sensing as input to infrastructural and agricultural development as they directly relate to flood control and disaster prevention in the Third World. The radar imagery collected for this project penetrated the latent monsoonal cloud cover and revealed hydrological conditions on the ground during severe weather. The radar data sets were used to generate areal measurements of the flooded/non-flooded land surfaces in Central Bangladesh, and in the coastal regions of Bangladesh, the vegetation penetrating ability of the radar was used to map soil topography and carrying capacity in mangrove forests.

SIR‐B observations of dominant ocean waves near Hurricane Josephine

Radar images of ocean surface waves near hurricane Josephine were acquired with the shuttle imaging radar B (SIR‐B) system on October 12, 1984. Fast Fourier transform analyses of the images have been performed along most of the 600‐km image track. These data reveal the presence of at least two dominant wave systems which undergo significant spatial variations in wavelength and direction.

Preliminaly Evaluation of the SIR-B Response to Soil Moisture, Surface Roughness, and Crop Canopy Cover

stract-Two pre-dawn ascending data-akes (dt. 49.2 and 97.2) by the Shuttle Imaging Radar (SIR-B) are used to evaluate the effects of soil moisture, surface roughness, and crop canopy cover on radar backscattering. The two images are separated in acquisition date by three days and were obtained at the same local angle of incidence (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 30°) but with opposite azimuth viewing directions (Δα = 180°). The digitally recorded and processed SIR-B imagery is externallyi-calibrated with respect to the radar backscattering coefficient σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> via response to arrays of point and area-extended targets of known radar cross section. Extensive ancillary data pertaining to scene physical and biophysical al conditions were collected from approximately 400 agricultural fields within a 20 km × 20 km test site in west-central Illinois. The test site was largely agricultural and consisted primarily of corn and soybeans at harvest-ready conditions. For the agricultural portions of the scene, σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> is found to vary over a 16-to 20-dB dynamic range for a given observation date. The magnitude of σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> is found to be proportional to soil moisture, surface roughness, and canopy biomass. Although the SIR-B sensor parameters es ( L-band, HH polarization, θnd 0 ° 300) were not expected to be optimum for estimation of near-surface soil moisture, significant linear correlations are observed between σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> (in decibels) and 0-5-cm volumetric moisture m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v. For a given target class as broadly defined by surface roughness and canopy cover, linear regression of σ⁰_SIR-B (dB) to m&#x01d52f; generally yields correlation coefficients of &#x01d52f;² ≃ 0.8.</sub>

Comparison of Simulated and Measured Synthetic Aperture Radar Image Spectra with Buoy-Derived Ocean Wave Spectra During the Shuttle Imaging Radar B Mission

During the SIR-B mission over the North Sea, two successful synthetic aperture radar (SAR) data takes with simultaneous buoy measurements of ocean wave spectra have been obtained on October 6 and 8, 1984. On October 6, the SAR imaging of ocean waves was predicted as strongly nonlinear and on October 8 as almost linear. The SIR-B experiment confirmed the theoretical predictions. By applying the SAR imaging model based on velocity bunching theory the SAR image spectra are calculated from the measured ocean wave spectra. These calculated SAR image spectra are compared with the SIR-B derived SAR image spectra and it is shown that both agree quite well. This is considered as a further experimental confirmation for the velocity bunching model that has been proposed for describing SAR imaging of ocean surface waves.

Microwave Penetration and Attenuation in Desert Soil: A Field Experiment with the Shuttle Imaging Radar

Receivers buried in the Nevada desert were used with the Shuttle Imaging Radar to measure microwave attenuation as a function of soil moisture in situ. Results agree closely with laboratory measureements of attenuation and suggest that penetration of tens of centimeters in desert soils is common for L-band (1.2-GHz) radar.

SIR-B-The Second Shuttle Imaging Radar Experiment

On October 5, 1984, the second Shuttle Imaging Radar (SIR-B) was launched into orbit aboard the space shuttle Challenger. SIR-B is part of an evolutionary radar program designed to progressively develop a multifrequency, multipolarization synthetic aperture radar with a variable Earth-imaging geometry. The SIR-B instrument is an upgraded version of SIR-A, with the additional capability of tilting the antenna mechanically to acquire imagery at variable incidence angles ranging from 15°to 60°.The variable look angle capability provided a means of acquiring multiple incidence angle imagery over specific targets on successive days of the mission. These data are being used to classify surface features by their backscatter signatures as a function of incidence angle and for topographic mapping. In addition to the antenna tilt capability, a digital data-handling system was added to increase the dynamic range, the resolution was improved by a factor of two over SIR-A, and a calibration subsystem was added to improve the radiometric accuracy of the data. The mission had a number of problems, including loss of the primary mary digital data path between the shuttle and the ground. In spite of these problems, approximately 20 percent of the planned digital data were collected over the 8-day shuttle mission corresponding to an areal coverage of about 6.4 million km2.

On the Estimation of Wave Slope-and Height-Varnance Spectra from SAR Imagery

A procedure is described for using synthetic aperture radar (SAR) imagery to estimate two-dimensional ocean wave slope-and height-variance spectra. The logic underpinning the procedure is based both on the results of the numerical simulation of SAR wave imagery and analytic descriptions of the SAR imaging process. The procedure, when applied to SAR imagery of waves acquired during the recent Shuttle Imaging Radar Mission (SIR-B), is shown to produce spectra that agree with independent measures of both the two-dimensional slope-and height-variance spectra. The implications of these results for future SAR missions aimed at measuring ocean waves are considered.

Use Of Speckle For Determining The Response Characteristics Of Doppler Imaging Radars

The synthetic aperture radar (SAR) aboard Seasat in 1978 demonstrated a unique sensitivity to oceanic and geologic features imaged over a 100 km swath with 25 m resolution. The ability of the remote sensor to resolve the fine details of large environmental systems resulted in the orbiting of a similar system, the Shuttle Imaging Radar (SIR-B), aboard the Space Shuttle Challenger during October 1984. Coherent speckle noise observed for these Doppler imaging-radar systems is caused by random correlations of the illuminating radar chirp with the surface reflectance downrange. Radar speckle is similar to optical speckle in that respect, but it is also influenced by along-track sampling statistics. The Rayleigh statistics of coherent scattering and the Poisson statistics of radar pulse detection are employed to model the speckle observed in spatially random data samples. Speckle degradation of a radar scene may obstruct interpretations of scene detail, but it can also be useful in determining the spatial response of the remote sensor and scene correlator. Randomly speckled scenes that are otherwise featureless provide a white-noise input to the Doppler imaging process. Several such scenes have been processed with fast Fourier transform methods to estimate the point spread function and its Fourier-domain equivalent, the wavenumber response function. These measure-ments of spatial resolution are used to compare the Seasat SAR and the Challenger SIR-B remote sensors. In addition, two ground-scene correlators are compared in terms of the point spread estimate of spatial resolution for common input data from the SIR-B sensor.

Application of shuttle imaging radar data for land use investigations

A Shuttle Imaging Radar (SIR)-A image in the south of Tianjin acquired by the SIR-A in November 1981 was interpreted manually and with the aid of a computer system. The methods of processing involved density slicing with statistical training, producing normalized false color composite images through coregistration of the SIR-A and Landsat MSS image data sets, and unsupervised clustering. The interpretation keys for the SIR-A image were established after investigation in situ and analysis of soil dielectric and moisture properties. The interpretation accuracy for various images was determined by using a combination of color infrared aerial photography and land use maps acquired recently. The research indicates that the SIR-A data can remedy some defects of Landsat MSS data due to the SIR-A's better response to residential areas and linear features. The SIR-A/Landsat MSS normalized composite image incorporated the strong points of both. The interpretation accuracy, therefore was increased.

Speckle Suppression And Analysis For Synthetic Aperture Radar Images

Speckle appearing in synthetic aperture radar (SAR) images is generated by coherent interference of radar echoes from target scatters. Basically, speckle noise has the nature of a multiplicative noise. In this paper procedures for defining and verifying a statistical noise model are developed, and two multiplicative noise-smoothing algorithms are pre-sented. These two algorithms are computationally efficient and have the potential of achieving real-time or near-real-time processing. Several SEASAT SAR and SIR-B (Shuttle Imaging Radar) images are used for illustration.

Shuttle Imaging Radar: Physical Controls on Signal Penetration and Subsurface Scattenng in the Eastern Sahara

SIR-A signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the Eastern Sahara of southern Egypt and northern Sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials. Interpretation of SIR-A images by McCauley et al. [1], [2] dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat, featureless, and hyperarid landscape. In the present paper we summarize the near-surface stratigraphy, the electrical properties of materials, and the types of radar interfaces found to be responsible for different classes of SIR-A tonal response. The dominant factors related to efficient microwave signal penetration into the sediment blanket include a) favorable distribution of particle sizes, b) extremely low moisture content and c) reduced geometric scattering at the SIR-A frequency (1.3 GHz). The depth of signal penetration that results in a recorded backscatter, here called "radar imaging depth," was documented in the field to be a maximum of 1.5 m, or 0.25 of the calculated "skin depth," for the sediment blanket. Radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials. Diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops.

SIR-A views our environment An Experiment in the Batu Angkal Area, West Kalimantan, Indonesia

Cloud cover is a serious problem for remote sensing in Indonesia. Some areas, around 10% to 20% of the land territory, are almost never cloud-free. The only system of remote sensing capable of overcoming cloud cover problem is that applying microwave energy. This article deals with a radar system being operated by the Columbia shuttle imaging radar A in 1981 in the Batu Angkal area, West Kalimantan, Indonesia. The choice of the study area is due to the availability of collateral material such as topographic map. land use map, and false color photographs. The study is aimed at learning the interpretability of SIR-A image of 1:500,000 which is blown up to 1:250,000 for the study of the.environment of this area. The method used in the identification of environment is applying the physical characteristics of objects (tone, texture, shape, size, direction in relation to the illumination, surface roughness, and dielectric constant) to trace it. The discernable elements of the environment of the study area are listed sequentially based on the ease of identqicaiton: rivers and dissected hills, unpaind forest and lowland forest, wetfields, and road and settlement. Factors affecting the ease of identification are. mainly tonal contrast, shape, size, surface roughness, direction in relation to the illumination, and dielectric constant. Due to the future availability of SIR-B image of Kalimantan, further study is recommended.

SIR‐B iceberg observation

The Shuttle Imaging Radar (SIR) made its second flight (called SIR‐B) in October 1984. Among the 44 science projects that it was due to support were two ice‐related studies, one concerning the behavior of the sea ice of the southern ocean pack and marginal ice zones and another concerning the detectability of icebergs and other navigational hazards off the east coast of Canada. The southern ocean sea ice team was led by F. Carsey of the Jet Propulsion Laboratory (JPL), Pasadena, Calif., and consisted of B. Holt (JPL), S. Martin (University of Washington, Seattle), L. Mc‐Nutt (Radarsat, Ottawa), D.A. Rothrock (Polar Science Center, Seattle), W.F. Weeks (U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H.), and V. Squire (Canada Centre for Remote Sensing (CCRS), Ottawa); the iceberg team was led by A.L. Gray (CCRS) and consisted of J.Princz, C.E. Livingstone, R.K. Hawkins, M. Wong (all of CCRS), D. Pearson (Petro‐Canada Exploration, Calgary, Canada), J. Gower (Institute of Ocean Sciences, Sydney, Canada), T.F. Mullane, and R.O. Ramseier (both of the Atmospheric Environment Service, Ottawa). As it happened, the SIR‐B mission experienced difficulty with its data link to a geostationary relay satellite and with the SIR‐B radar transmitter, with the consequences that the total amount of data taken was only about one fifth of what was planned and that the data quality was impaired in comparison to what had been anticipated. The result was that no iceberg synthetic aperture radar (SAR) images off the Canadian coast and very limited sea ice SAR images in the southern ocean were acquired; however, a few interesting SAR images of the southern ocean icebergs were acquired, and a few of these are shown in Figure 1.

MAPPING WITH AIRCRAFT AND SATELLITE RADAR IMAGES

AbstractThe history of radargrammetry spans about 35 years. It has moved from early plan position indicator (PPI) radar records of 1948 to the current (1984) space shuttle imaging radar SIR‐B. We can look forward to the future 1989 European and Japanese remote sensing satellites ERS‐1 and NASA's 1988 Venus Radar Mapper (VRM) mission. The mapping application requires that methods be available to deal with single images, stereoscopic pairs or blocks of image strips. The predominantly digital data format suggests that radargrammetric methods should be implemented in digital image processing systems for rectification, digital terrain elevation extraction and multi‐image registration for change monitoring. This paper presents a review of current radargrammetric understanding, applications and expected developments.

Synthetic aperture radar and the SIR-8 program

Abstract The U.S. National Aeronautics and Space Administration (NASA) is actively involved in the development of spaceborne synthetic aperture radar systems. Its program has included the launch of Seasat in 1978, Shuttle Imaging Radar A (SIR-A) in 1981, and the most recent SIR-B in October of 1984. This paper briefly outlines the latter program and gives details of a number of experiments being conducted by the Centre for Remote Sensing and Associated Schools at the University of New South Wales, as part of a series of worldwide SIR-B experiments. Greatest emphasis is given to those experiments relating to topographic mapping and urban monitoring. Some theoretical aspects of imaging radar systems and synthetic aperture radar in particular, are given to provide the reader with a background to this new technology.

SIR-A imagery of Tunisia and its potential for population estimation.

The value of Shuttle Imaging Radar images for the estimation of population is considered using a 1981 example for Tunisia. The results are compared with 1975 census data. The results show that the relationship of image areas to population is reasonably strong in areas where settlements are relatively small and have a uniform and low building density.

Natural oil seep detection in the Santa Barbara Channel, California, with Shuttle Imaging Radar

Natural submarine oil seeps in the Santa Barbara Channel, California, were detected by the first Shuttle Imaging Radar (SIR-A). Oil slicks on the ocean are seen in radar imagery as areas of decreased radar signal return that result from a damping of surface roughness. Orbital radar imagery shows promise as an effective and efficient means of mapping submarine oil seeps as sources of naturally occurring oil slicks.