Theory of passive remote sensing with microwaves
Theoretical models are described which were developed for use in the interpretation of microwave data from the earth's surface.
Kong, J. A.↗
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Sensors and methods for weather-independent remote sensing with microwaves
Sensors and methods of radar and microwave radiometry which operate in the millimeter wave range are discussed. The properties of electromagnetic waves are discussed as well as the resolution capacity and measurement accuracy of sensor systems.
Keydel, W.↗
Atmospheric Remote Sensing by Microwave Radiometry
The Earth's atmosphere is a puzzle and a concern. Its unpredictable weather has always been a force to be recokoned with, but until recent times, our trust was implicit in the robustness of the atmospheric system as the foundation of our biosphere. Now we are not so sure.
microwave↗
Improving cold-region streamflow estimation by winter precipitation adjustment using passive microwave snow remote sensing datasets
Explore the source record for details and available documents.
D Kang↗
In-situ measurements for validation of microwave data - Problems, accuracies
This review covers the relationship between remotely sensed microwave data and data obtained in situ or from earth-based remote-sensing systems, both for validation of algorithms and as supplemental information for deriving a geophysical quantity. Parameters obtained from satellite microwave radiometers, the Scanning Multichannel Microwave Radiometer, and the Special Sensor Microwave Imager are emphasized. These include sea-surface temperature and wind speed, integrated atmospheric water vapor, cloud liquid water, and rain rate.
Katsaros, Kristina B.↗
AMSR2 Soil Moisture Downscaling Using Temperature and Vegetation Data
Soil moisture (SM) applications in terrestrial hydrology require higher spatial resolution soil moisture products than those provided by passive microwave remote sensing instruments (grid resolution of 9 km or larger). In this investigation, an innovative algorithm that uses visible/infrared remote sensing observations to downscale Advanced Microwave Scanning Radiometer 2 (AMSR2) coarse spatial resolution SM products was developed and implemented for use with data provided by the Advanced Microwave Scanning Radiometer 2 (AMSR2). The method is based on using the Normalized Difference Vegetation Index (NDVI) modulated relationships between day/night SM and temperature change at corresponding times. Land surface model output variables from the North America Land Data Assimilation System (NLDAS), remote sensing data from the Moderate-Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) were used in this methodology. The functional relationships developed using NLDAS data at a grid resolution of 12.5 km were applied to downscale AMSR2 JAXA (Japan Aerospace Exploration Agency) SM product (25 km) using MODIS land surface temperature (LST) and NDVI observations (1 km) to produce the 1 km SM estimates. The downscaled SM estimates were validated by comparing them with ISMN (International Soil Moisture Network) in situ SM in the Black Bear-Red Rock watershed, central Oklahoma between 2015-2017. The overall statistical variables of the downscaled AMSR2 SM validation R2, slope, RMSE and bias, demonstrate good accuracy. The downscaled SM better characterized the spatial and temporal variability of SM at watershed scales than the original SM product.
AMSR2; passive microwave soil moisture; soil moist↗
The sensitivity of synthetic aperture radiometers for remote sensing applications from space
Aperture synthesis offers a means of realizing the full potential microwave remote sensing from space by helping to overcome the limitations set by antenna size. The result is a potentially lighter, more adaptable structure for applications in space. However, because the physical collecting area is reduced, the signal-to-noise ratio is also reduced and may adversely affect the radiometric sensitivity. Sensitivity is an especially critical issue for measurements from low earth orbit because the motion of the platform (about 7 km/s) limits the integration time available for forming an image. The purpose of this paper is to develop expressions for the sensitivity of remote sensing systems which use aperture synthesis. The objective is to develop basic equations general enough to be used to obtain the sensitivity of the several variations of aperture synthesis which have been proposed for sensors in space. The conventional microwave imager (a scanning total power radiometer) is treated as a special case, and the paper concludes with a comparison of three synthetic aperture configurations with the conventional imager.
Le Vine, David M.↗
Microwave sensors for earth resource observations in the 1980's
Future trends in microwave sensing are identified with reference to the workshops organized by the Active Microwave Remote Sensing Research Program. The workshops demonstrated that (1) microwave techniques have great potential for earth observations of renewable and nonrenewable resources and (2) existing research does not adequately assess microwave sensor measurement capabilities. The need for synoptic information includes such areas as cloud-free, surface-roughness and electrical-properties data. Attention is given to applications including all-weather imaging, sensitivity to vegetation and soil-moisture conditions. Research tasks to be accomplished during the next five years are discussed.
Rouse, J. W., Jr.↗
The sensitivity of synthetic aperture radiometers for remote sensing applications from space
Aperture synthesis offers a means of realizing the full potential of microwave remote sensing from space by helping to overcome the limitations set by antenna size. The result is a potentially lighter, more adaptable structure for applications in space. However, because the physical collecting area is reduced, the signal-to-noise ratio is reduced and may adversely affect the radiometric sensitivity. Sensitivity is an especially critical issue for measurements to be made from low earth orbit because the motion of the platform limits the integration time available for forming an image. The purpose is to develop expression for the sensitivity of remote sensing systems which use aperture synthesis. The objective is to develop basic equations general enough to be used to obtain the sensitivity of the several variations of aperture synthesis which were proposed for sensors in space. The conventional microwave imager (a scanning total power radiometer) is treated as a special case and a comparison of three synthetic aperture configurations with the conventional imager is presented.
Levine, D. M.↗
Polarimetric emission from anisotropic media for passive remote sensing of sea ice
The polarimetric emission from an anisotropic medium with applications to the passive microwave remote sensing of sea ice is investigated. Based on the fluctuation-dissipation theory, the Stokes vector is obtained for the thermally exicted electromagnetic radiation from an anisotropic object. By modeling sea ice as a layered anisotropic medium, the Stokes vector representing the polarimetric emission is illustrated for various geophysical conditions. It is found that the difference in the brightness temperatures measured at two surface temperatures is correlated with the thickness of the sea ice. For cases where the c-axis of sea ice is aligned or not random in the horizontal plane, the calculated brightness temperatures show a periodic variation when plotted as a function of the azimuthal angle of the observation direction, indicating that the polarimetric Stokes parameters can be used to detect the direction of c-axes in sea ice.
Yueh, S. H.↗
Remote sensing of soil moisture
Four major objectives are proposed: (1) to study the sensitivity of active and passive microwave remote sensing approaches to soil moisture variations; (2) to investigate the effect of vegetation cover on microwave backscatter and emission; (3) to test theoretical models of microwave backscatter and emission from a natural terrain against the observations obtained from SIR-B and aircraft radiometer flights; and (4) to estimate vegetation biomass with airborne visible and infrared sensors.
Wang, J. R.↗
(abstract) Tropospheric Calibration for the Mars Observer Gravity Wave Experiment
In spring 1993, microwave radiometer-based tropospheric calibration was provided for the Mars Observer gravitational wave search. The Doppler shifted X-band radio signals propagating between Earth and the Mars Observer satellite were precisely measured to determine path length variations that might signal passage of gravitational waves. Experimental sensitivity was restricted by competing sources of variability in signal transit time. Principally, fluctuations in the solar wind and ionospheric plasma density combined with fluctions in tropospheric refractivity determined the detection limit. Troposphere-induced path delay fluctions are dominated by refractive changes caused by water vapor inhomogeneities blowing through the signal path. Since passive microwave remote sensing techniques are able to determine atmospheric propagation delays, radiometer-based tropospheric calibration was provided at the Deep Space Network Uranus tracking site (DSS-15). Two microwave water vapor radiometers (WVRs), a microwave temperature profiler (MTP), and a ground based meterological station were deployed to determine line-of-sight vapor content and vertical temperature profile concurrently with Mars Observer tracking measurements. This calibration system provided the capability to correct Mars Observer Doppler data for troposphere-induced path variations. We present preliminary analysis of the Doppler and WVR data sets illustrating the utility of WVRs to calibrate Doppler data. This takes an important step toward realizing the ambitious system required to support future Ka-band Cassini satellite gravity wave tropospheric calibration system.
atmospheric water vapor microwave remote sensing↗
Forward Electromagnetic Scattering Models for Sea Ice
Recent advances in forward modeling of the electromagnetic scattering properties of sea ice are presented. The results have direct relevance to microwave remote sensing, and serve at the basis for inverse algorithms for reconstructing the physical properties of sea ice from scattering data.
Electromagnetic↗
Exploring scaling issues by using NASA Cold Land Processes Experiment(CLPX-1, IOP3) radiometric data
The NASA Cold-land Processes Field Experiment-1 (CLPX-1) involved several instruments in order to acquire data at different spatial resolutions. Indeed, one of the main tasks of CLPX-1 was to explore scaling issues associated with microwave remote sensing of snowpacks. To achieve this task, microwave brightness temperatures collected at 18.7, 36.5, and 89 GHz at LSOS test site by means of the University of Tokyo s Ground Based Microwave Radiometer-7 (GBMR-7) were compared with brightness temperatures recorded by the NOAA Polarimetric Scanning Radiometer (PSR/A) and by SSM/I and AMSR-E radiometers. Differences between different scales observations were observed and they may be due to the topography of the terrain and to observed footprints. In the case of satellite and airborne data, indeed, it is necessary to consider the heterogeneity of the terrain and the presence of trees inside the observed scene becomes a very important factor. Also when comparing data acquired only by the two satellites, differences were found. Different acquisition times and footprint positions, together with different calibration and validation procedures, can be responsible for the observed differences.
Tedesco, Marco↗
Large space antenna technology applied to radar-imaging, rain-rate measurements, and ocean wind sensing
During the last decade, the utility of spaceborne microwave remote sensing systems for ocean windspeed measurement, ocean wave imaging and sea ice studies was demonstrated. Development of large space antennas offers some interesting possibilities for rain rate measurements, ocean and ice studies, and radar imaging. The joint use of active and passive sensors using the 15 m antenna for ocean, ice, and soil moisture studies; rain rate measurements; and radar imaging is considered. Verification of the frequency agile rain radar concept with Shuttle offers the possibility of much needed rain rate statistics over the ocean.
Moore, R. K.↗
The DMRT-ML Model: Numerical Simulations of the Microwave Emission of Snowpacks Based on the Dense Media Radiative Transfer Theory
Microwave radiometer observations have been used to retrieve snow depth and snow water equivalent on both land and sea ice, snow accumulation on ice sheets, melt events, snow temperature, and snow grain size. Modeling the microwave emission from snow and ice physical properties is crucial to improve the quality of these retrievals. It also is crucial to improve our understanding of the radiative transfer processes within the snow cover, and the snow properties most relevant in microwave remote sensing. Our objective is to present a recent microwave emission model and its validation. The model is named DMRT-ML (DMRT Multi-Layer).
Microwave radiometer↗
The DMRT-ML Model: Numerical Simulations of the Microwave Emission of Snowpacks Based on the Dense Media Radiative Transfer Theory
Microwave radiometer observations have been used to retrieve snow depth and snow water equivalent on both land and sea ice, snow accumulation on ice sheets, melt events, snow temperature, and snow grain size. Modeling the microwave emission from snow and ice physical properties is crucial to improve the quality of these retrievals. It also is crucial to improve our understanding of the radiative transfer processes within the snow cover, and the snow properties most relevant in microwave remote sensing. Our objective is to present a recent microwave emission model and its validation. The model is named DMRT-ML (DMRT Multi-Layer), and is available at http:lgge.osug.frpicarddmrtml.
ice sheet↗
Spaceborne Radar Remote Sensing: Radar Interferometry, Scatterometry and Altimetry
Spaceborne remote sensing instruments allow the acquisition of global and synoptic information for Earth Science investigations. In particular, active microwave remote sensing that have contributed geophysical measurements of a scale and accuracy which surpass what could be accomplished with ariborne or in-situ observations.
Spaceborne Radar Remote Sensing Interferometry↗