Microwave radiometers for ocean and weather measurements. part i- summary discussion of microwave radiometry
Microwave radiometers for ocean and weather measurements
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The Advanced Microwave Radiometer – Climate Quality (AMR-C) Instrument for Sentinel-6
The Advanced Microwave Radiometer – Climate Quality (AMR-C) is designed to measure the path delay due to atmospheric water vapor along Sentinel-6 altimeter path over one decade. The AMR-C receiver is based on heritage from previous AMR instruments with the addition of a THz-frequency radiometer, the High Resolution Microwave Radiometer (HRMR), for improved coastal zone accuracy and a Supplemental Calibration System (SCS) to meet level 3 requirements that the path delay error due to the altimeter-derived sea surface height be less at 0.8 cm and the path delay stability be maintained to 0.7 mm averaged over a 1-year time period.
Maiwald, Frank↗
Multi-Channel Correlator Array-Fed Microwave Radiometer
Multiband passive microwave imagery in X to W Bands has a nearly 40-year history of utilization for measurement of multiple geophysical parameters (e.g., precipitation rate, ocean surface wind speed, sea ice concentration, and land surface temperature). Spatial resolution is limited by aperture size, and although aperture sizes have grown to 1-2 meters, current capability will not meet future spatial resolution needs. As aperture size increases, new antenna feed techniques are needed to maintain contiguous coverage and obtain Nyquist sampling. Here we apply the correlator array fed radiometer architecture adapted from radio astronomy and show how it can meet emerging needs. Simulation results of a 0.8-m, 36.5-GHz, array-fed reflector (equivalent to 20 meters at 1.41 GHz) show the feasibility of creating multiple over-lapping beams.
Microwave radiometer↗
Antenna pattern corrections to microwave radiometer temperature calculations
In making microwave radiometer calculations of sea surface temperature, it is necessary to consider the errors resulting from the antenna radiation pattern. This is especially true for antennas with high sidelobes that are scanned in viewing angle and for antennas with high cross-polarized components. It is concluded that the plane wave brightness temperature is not by itself sufficient to describe the true radiometer temperature of the sea surface. This discrepancy can be attributed to one or more of the following: failure to use the total radiation pattern, error in determining the sea surface dielectric constant, error in sky model profile, or radiation pattern spillover onto water surroundings.
Beck, F. B.↗
Scanning mechanism study for multi-frequency microwave radiometers
Scanning mode for a microwave radiometer having large aperture antenna is determined from scientific needs by engineering tradeoffs. Two configurations of the scan drive mechanism with an integral momentum compensation are formulated for 1.OM and 1.4M diameter antennas. As the formulation is based on currently available components, it is possible to design and fabricate the formulated mechanism without new hardware development. A preliminary specification for major components of formulated drives is also included in the report.
Shin, I.↗
A 15-meter deployable aperture microwave radiometer
The Large Antenna Multifrequency Microwave Radiometer (LAMMR) was a 4-meter-diameter mechanically scanned (at 1 rps) antenna operating at frequencies from 4.3 to 36 GHz. This LAMMR system was scheduled to fly on the National Oceanic Satellite System (NOSS) in 1986 to measure sea surface temperature and wind speed along with several other atmospheric and sea ice parameters. The LAMMR was limited to a 4-meter solid reflector to stay within the Shuttle/NOSS launch volume and to operate with radiometric precision up to 36.5 GHz. Under the 4-meter aperture constraint, LAMMR could not meet the user resolution requirement for sea surface temperature (25 km minimum, 50 km goal) in an RFI free band, i.e., 4.3 GHz. This study explores the feasibility of meeting this requirement goal with a 15-meter mechanically scanned deployable reflector. Two other research objectives can also be studied by adding one active (approximately 5 GHz) and two additional passive (1.4 and 6.4 GHz) channels to investigate soil moisture and precipitation profiles over land. These two objectives are closely related because the precipitation is the source of the soil moisture in unirrigated regions, and the soil moisture changes between samples (2/day) could indicate that precipitation may have occurred while the sensor was not in view.
Coyner, J. V., Jr.↗
Passive microwave radiometer experiment for GOES-NEXT
A new passive microwave radiometer (PMR) experiment for GOES-NEXT is described. The PMR, expected to be in orbit in the early 1990's, is a multichannel microwave radiometer which will allow new measurements of temperature and moisture structure and precipitation by penetrating much of the overlying cloud cover near significant weather systems. PMR experimental objectives are to use a geostationary platform for the first time to obtain passive microwave imagery and soundings in a high time frequency mode to address several scientific objectives. These scientific objectives address current problems of atmospheric science at the mesoscale and in climate research.
Vonder Haar, Thomas H.↗
Multifrequency microwave radiometer measurements of soil moisture
Ground-based microwave radiometer experiments are carried out to investigate the effects of moisture, temperature, and roughness on microwave emission from bare soils. The measurements are made at frequencies of 0.6-0.9, 1.4, and 10.7 GHz using van-mounted radiometers to observe prepared soil sites in Kern County, CA. Brightness temperature variations of approximately 15 K at 1.4 GHz and 25 K at 10.7 GHz are observed as a result of diurnal changes in the soil temperature. Increasing the soil moisture content from 2% to 15% by volume is found to result in brightness temperature decreases of approximately 70 K at 0.775 and 1.4 GHz and 40 K at 10.7 GHz, depending, to a lesser extent, on polarization and viewing angle. The results attest the significance of soil temperature in deriving soil moisture from microwave radiometer measurements. Comparisons of the microwave measurements with theoretical predictions using smooth surface models give reasonable agreement and support previous results of this nature obtained with other soil types.
Njoku, E. G.↗
Preliminary results from aircraft flight tests of an electrically scanning microwave radiometer
Aircraft flight tests of electric scanning microwave radiometer designed for meteorological satellite
SCANNING DEVICE↗
Design and Results of Differential Microwave Radiometers (DMR) on COBE
The Differential Microwave Radiometer (DMR) experiment on the Cosmic Background Explorer is in the final year of a scheduled four years of operation to measure large- and intermediate-scale anisotropies in the Cosmic Microwave Background (CMB). The DMR instrument comprises two independent radiometers at each of three frequencies, 31.5 53, and 90 GHz, where the frequencies were chosen to best separate the CMB from the foreground emissions from galactic dust and electrons...
Kogut, Alan J.↗
The microwave radiometer spacecraft. A design study: Executive summary
A conceptual design was developed for a microwave radiometer spacecraft (MRS) using a large passive reflector, microwave radiometer, and advanced control concepts soil moisture mapping from microwave sensing for global crop forecasting. Mission requirements and tradeoffs were defined, and major subsystems (structural, electromagnetic surface, and attitude control) conceptually designed. An overview of the mission and a summary of the study results are presented.
Lovelace, U. M.↗
Electrically scanning microwave radiometer for Nimbus E
An electronically scanning microwave radiometer system has been designed, developed, and tested for measurement of meteorological, geomorphological and oceanographic parameters from NASA/GSFC's Nimbus E satellite. The system is a completely integrated radiometer designed to measure the microwave brightness temperature of the earth and its atmosphere at a microwave frequency of 19.35 GHz. Calibration and environmental testing of the system have successfully demonstrated its ability to perform accurate measurements in a satellite environment. The successful launch and data acquisition of the Nimbus 5 (formerly Nimbus E) gives further demonstration to its achievement.
Source record↗
Rainfall estimation over oceans from scanning multichannel microwave radiometer and special sensor microwave/imager microwave data
The brightness temperature (T sub b) measured at 37 GHz shows fairly strong emission from rain, and only slight effects caused by scattering by ice above the rain clouds. At frequencies below 37 GHz, were the fov is larger and the volume extinction coefficient is weaker, it is found that the observations do not yield appreciable additional information about rain. At 85 GHz (fov = 15 km), where the volume extinction is considerably larger, direct information about rain below the clouds is usually masked. Based on the above ideas, 37 GHz observations with a 30 km fov from SMMR and SSM/I are selected to develop an empirical method for the estimation of rain rate. In this method, the statistics of the observed T sub b's at 37 GHz in a rain storm are related to the rain rate statistics in that storm. The underestimation of rain rate, arising from the inability of the radiometer to respond sensitively to rain rate above a given threshold, is rectified in this technique with the aid of two parameters that depend on the total water vapor content in the atmosphere. The retrieved rain rates compare favorably with radar observations and monthly mean global maps of rain derived from this technique over the oceans.
Prabhakara, C.↗
Remote Sensing of Ocean Wind Using Polarimetric Microwave Radiometers
Winds over the ocean modulate the air-sea fluxes of heat, moisture, gases and particulates, regulating the crucial coupling between atmosphere and ocean that establishes and maintains global and regional climate. Global mapping (using spaceborne scatterometers) of ocean wind is crucial for many oceanographic and atmospheric studies. An overview of polarimetric wind radiometer (new) technology is given.
Ocean Ocean Wind Remote Sensing Radiometer Microwa↗
COBE Differential Microwave Radiometers - Instrument design and implementation
Differential Microwave Radiometers (DMRs) at frequencies of 31.5, 53, and 90 GHz have been designed and built to map the large angular scale variations in the brightness temperature of the cosmic microwave background radiation. The instrument is being flown aboard NASA's Cosmic Background Explorer (COBE) satellite, launched on November 18, 1989. Each receiver input is switched between two antennas pointing 60 deg apart on the sky. The satellite is in near-polar orbit with the orbital plane precessing at 1 deg per day, causing the beams to scan the entire sky in 6 months. In 1 year of observation, the instruments are capable of mapping the sky to an rms sensitivity of 0.1 mK per 7 deg field of view. The mission and the instrument have been carefully designed to minimize the need for systematic corrections to the data.
Smoot, G.↗
Preliminary development of digital signal processing in microwave radiometers
Topics covered involve a number of closely related tasks including: the development of several control loop and dynamic noise model computer programs for simulating microwave radiometer measurements; computer modeling of an existing stepped frequency radiometer in an effort to determine its optimum operational characteristics; investigation of the classical second order analog control loop to determine its ability to reduce the estimation error in a microwave radiometer; investigation of several digital signal processing unit designs; initiation of efforts to develop required hardware and software for implementation of the digital signal processing unit; and investigation of the general characteristics and peculiarities of digital processing noiselike microwave radiometer signals.
Stanley, W. D.↗
Meteorological interpretations of the images from the Nimbus 5 electrically scanned microwave radiometer
The Nimbus 5 Electrically Scanned Microwave Radiometer (ESMR) is useful in determining the extent, structure, and intensity of rainfall over oceans. It is possible on the basis of rainfall maps to determine the location of frontal rain, rain/snow boundaries, and the structure of tropical storms. ESMR data on rainfall over the east coast of the United States and the Gulf of Mexico, on snowfall over the northeast coast of the United States, on frontal zones in the northwestern Pacific and on the tropical storm Leila in the South Indian Ocean are examined. Because of the generally high emissivities of land surfaces, interpretation of meteorological parameters over land is not yet possible.
Wilheit, T. T.↗
Tropical cyclone rainfall characteristics as determined from a satellite passive microwave radiometer
Data from the Electrically Scanning Microwave Radiometer on Nimbus-5 (ESMR-5) have been used to calculate total tropical cyclone Latent Heat Release (LHR) and rainfall parameters for over 70 satellite observations of 21 tropical cyclones during 1973, 1974, and 1975 in the North Pacific tropical ocean. The data were found to be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring and making short-term prediction of their intensity. Case studies as well as composite studies indicate that the increase in the ESMR-5 derived LHR corresponds to storm intensification. It also appears that the ESMR-5 derived rainfall parameters can be used to detect the beginning of tropical cyclone intensification.
Rodgers, E. B.↗