Microwave Imaging Radiometer Research Articles

Multifrequency polarimetric synthetic aperture radar observations of sea ice

The first known fully polarimetric airborne synthetic aperture radar (SAR) data set of sea ice is introduced. Images were acquired in the Beaufort, Bering and Chukchi seas in March 1988, during a campaign for validation of Defense Meteorological Satellite Program Special Sensor Microwave Imager radiometer ice products. Statistics of the magnitude, phase and polarization of complex backscattered signals recorded by the Jet Propulsion Laboratory three‐frequency SAR are examined in detail for various scenes with different ice characteristics. The full Stokes matrix information generated from C, L, and P band data characterize the scattering behavior of different ice types. Polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics. Results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency, fixed polarization micro‐wave radar. A specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ERS‐1 5.3GHz, VV polarization SAR data. Such findings are consistent with theoretical model simulations of scattering characteristics of sea ice. Overall, these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods.

Computation of Three-dimensional Radiometric Signals Detected in Microwave Imaging

AbstractThe present development of microwave radiometry for medical applications encourages the development of methods for computer modelling of the radiometric thermal signals transmitted by living tissues. This method, considers both homogeneous and multilayered tissues. We present here computed data for the definition of microwave radiometric imaging and for the interpretation of radiometric data.

Microwave radiometric imaging at 3 GHz for the exploration of breast tumors

A process of microwave radiometric imaging at 3 GHz permits the mapping of radiometric intensities on a square area about half a decimeter on a side. These data, translated in terms of a colored image, point out the existence of lateral temperature gradients in tissues. This system was initially used for examining large breast tumors; at present, it is also used for detecting smaller, impalpable tumors. The rules for characterizing benignancy or malignancy of small tumors which appear in a mammographic examination (X-rays) are defined. The definition of an appropriate parameter, deduced from this image processing, makes it possible to indicate benignancy or malignancy. In experiments conducted on 18 patients, all the malignant lesions had a radiometric ratio greater than 65%, while benign lesions were below 55%. However, a zone of uncertainty (between 55% and 70%) exists where it is wise not to assert malignancy or benignancy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Development of Airborne/ground-based 13mm Imaging Microwave Radiometer Using Two Reference Temperatures with Automatic Gain Compensation

The Development of Airborne/ground-based 13mm Imaging Microwave Radiometer Using Two Reference Temperatures with Automatic Gain Compensation

Optimum interpolation of imaging microwave radiometer data

A technique of interpolating imaging microwave radiometer data is presented as an application of the Backus-Gilbert theory. The interpolation process is optimal in the sense that it attempts to preserve the spatial resolution of the antenna gain function associated with the sampled radiometer data. The technique is applied to the Special Sensor Microwave/Imager (SSM/I) satellite data and is found to enhance the high-resolution features of the imagery. >

Snow Cover of the Upper Colorado River Basin from Satellite Passive Microwave and Visual Imagery

A comparison of passive microwave images from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) and visual images from the Defense Meteorological Satellite Program (DMSP) of the Upper Colorado River Basin shows that passive microwave satellite imagery can be used to determine the extent of the snow cover. Eight cloud-free DMSP images throughout the winter of 1985-1986 show the extent of the snowpack, which, when compared to the corresponding SMMR images, determine the threshold microwave characteristics for snow-covered pixels. With these characteristics, the 27 sequential SMMR images give a unique view of the temporal history of the snow cover extent through the first half of the water year. Beginning mid-November, the snow-covered area rapidly increases from near zero to 80 percent by the middle of January. During late February the snow-covered area decreases as a result of basin-wide warming. The microwave determinations initially overestimate the decrease in snow cover, as a result of liquid water in the snowpack, but the return of cooler temperatures restores the veracity of the passive microwave determinations.

Observations of precipitating convective systems at 92 and 183 GHz: Aircraft results

High spatial resolution data from an airborne microwave imaging radiometer operating at 92 and 183 GHz (0.32 and 0.16 cm wavelengths) are compared with ground-based radar data for a series of observations of precipitating convective systems. An inverse relationship between microwave brightness temperature (TB) and radar-derived rain rate (RR) is observed. Differences in the empirical curves between midlatitude and tropical cloud systems are related to the differing microphysical and dynamical environments.

An imaging microwave radiometer†

Abstract The phase A study of an imaging microwave radiometer (IMR) has been completed, for ESA, by a team of contractors led by BAe. The instrument design which was established during this study is described in this paper. The IMR would be able to measure the intensity of radiation in the microwave band at a number of specific frequencies. By a complex data retrieval process, some of the physical characteristics of the atmosphere and of the underlying surface may be extracted from such measurements. The instrument would view a limited area of the earth at any instant; this area is the instantaneous field of view (IFOV). By scanning the IFOV an image may be generated, and a conical scan would be used so that the incidence angle at the ground remains constant.

Ocean Experiments And Remotely Sensed Images of Chemically Dispersed Oil Spills

A series of experiments was performed at sea where the effectiveness of dispersants applied from a helicopter was tested on fresh and weathered crude oils released from a surface research vessel. In conjunction with these experiments, remote sensing measurements using an array of airborne optical and microwave sensors were performed in order to aid in the interpretation of the dispersant effectiveness and to obtain quantitative images of oil on the sea under controlled conditions. Surface oil thickness and volume are inferred from airborne measurements using a dual-channel microwave imaging radiometer, aerial color photography, and an airborne oceanographic lidar. The remotely sensed measurements are compared with point sampled data obtained using a research vessel. The mass balance computations of surface versus subsurface oil volume using remotely sensed and point sampled data are consistent with each other and with the volumes of oil released. Data collected by the several techniques concur in indicating that, for the oils used and under the sea conditions encountered, the dispersant and application method are primarily useful when applied to fresh oil.