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A number of topics supporting the systems analysis of a multifrequency aperture-synthesizing microwave radiometer system are discussed. Fellgett's (multiple) advantage, interferometer mapping behavior, mapping geometry, image processing programs, and sampling errors are among the topics discussed. A FORTRAN program code is given.
A relatively simple model for the microwave brightness temperature of sea surface Sun glitter is presented. The model is an accurate closeform approximation for the fourfold Sun glitter integral. The model computations indicate that Sun glitter contamination of on orbit radiometer measurements is appreciable over a large swath area. For winds near 20 m/s, Sun glitter affects the retrieval of environmental parameters for Sun angles as large as 20 to 25 deg. The model predicted biases in retrieved wind speed and sea surface temperature due to neglecting Sun glitter are consistent with those experimentally observed in SEASAT SMMR retrievals. A least squares retrieval algorithm that uses a combined sea and Sun model function shows the potential of retrieving accurate environmental parameters in the presence of Sun glitter so long as the Sun angles and wind speed are above 5 deg and 2 m/s, respectively.
A rigid body analysis of a baseline Large Space System (LSS) which is to function as a radiometer is presented. The LSS is placed in circular orbit about the Earth at an altitude of 650 km, subjected to environmental and vehicle interaction forces and torques, without an active control system of any type on board. The environment forces and torques are gravity gradient, solar radiation, and aerodynamic. Normal operation is in nadir pointing along the Z-local vertical axis. Orbital velocity is assigned to the x-axis of the spacecraft. The analysis is then used to demonstrate the ability or lack of the gravity gradient torques to stabilize the LSS over one complete orbit.
Two visible infrared spin scan radiometer (VISSR) instruments provided for the Geostationary Operational Environmental Satellite B and C (GOES B and C) spacecrafts are described. The instruments are identical to those supplied previously are summarized. A significant number of changes primarily involving corrections of drawing errors and omissions were also performed. All electrical changes were breadboarded (where complexity required this), were incorporated into the test module, and subjected to verification of proper operation throughout fall instrument temperature range. Evaluation of the changes also included design operating safety margins to account for component variations and life.
The data base software system, LARSPEC, is discussed and the data base format for agronomic, meteorological, spectroradiometer, and multiband radiometer data is described. In addition, the contents and formats of each record of data and the wavelength tables are listed and the codes used for some of the parameters are described.
A multiband radiometer suitable for operation from helicopter, small plane, truck, or tripod platforms was developed. The standard unit is equipped with the seven thematic mapper spectral bands with an added band from 1.5 to 1.30 microns; however, up to eight user specified bands from 0.4 to 15 microns may be installed under clean field conditions. Results of prototype tests of the spectral responsivity of the detectors, the transmittance of the optical filters as a function of wavelength, the fields of view, and the system linearity, temperature stability, noise performance, and dynamic range were evaluated. Minor modifications were made to the instrument and the results of final testing are reported.
The ability to conduct soundings from a geostationary platform has been demonstrated with the Visible IR spin-scan radiometer Atmospheric Sounder (VAS) aboard GOES-4. While a negative offset reaching 2.0-3.0 C for the upper atmospheric CO2 bands of VAS was observed in comparisons with High Resolution IR Radiation Sounder (HIRS) measurements and analyses of radiosonde data, VAS radiances are consistent with that material. After removing the offset, the temperature profiles derived from VAS radiances agree very well with those observed by radiosondes. Time variations in the atmospheric state are discernible from VAS soundings at three-hour intervals, and were confirmed by radiosonde observations.
A multichannel scanning radiometer developed for remote observation of cloud physical properties is described. Consisting of six channels in the near infrared and one channel in the thermal infrared, the instrument can observe cloud physical parameters such as optical thickness, thermodynamic phase, cloud top altitude, and cloud top temperature. Measurement accuracy is quantified through flight tests on the NASA CV-990 and the NASA WB-57F, and is found to be limited by the harsh environment of the aircraft at flight altitude. The electronics, data system, and calibration of the instrument are also discussed.
The images with geometric control which present Pioneer 10 and 11 Infrared Radiometer data aquired at Jupiter are compared with 5.0-micron and visible images taken in the same time frame. It is found that (1) at 5.0, 20 and 45 microns, the association of dark and light areas with warm and cool areas, respectively, extends to nearly all features observed on the planet; (2) where the normal association of light and dark visible markings with the zone velocity breaks down, the infrared emission seems to follow the visible cloud structure rather than the zonal velocity structure; and (3) exceptions to the general rule involve 20-micron radiation, which reflects conditions in the 0.1-0.3 bar altitude range. A comparison of Pioneer 10 and 11 images suggests that the South Equatorial Belt became brighter at 20 microns, yet remained constant at other wavelengths between the two encounters.
Investigations have been conducted concerning the development of new cavity pyrheliometer for an absolute measurement of solar irradiance both in preflight testing of spacecraft and in flight experiments to measure the total solar flux. A series of instruments developed as part of this program are electrically self-calibrated cavity pyrheliometers whose mode of operation is characterized by the name Active Cavity Radiometer (ACR). The temperatures of their cavity sensors are servocontrolled, actively maintained at constant temperatures relative to their heat sinks by electrical heating. The solar irradiance is related to the International System of Units by measuring the difference in amount of electrical heating required with the cavity sensor alternately shaded and exposed to the sun. Studies conducted with the ACR are discussed. While variations of a few tenths of a percent in solar total irradiance lasting no more than a week or two have been detected, no long term trends were identified.
A method for inferring carbon monoxide concentrations from gas filter radiometer data is presented. The technique can closely approximate the results of more costly line-by-line radiative transfer calculations over a wide range of altitudes, ground temperatures, and carbon monoxide concentrations. The technique can also be used over a larger range of conditions than those used for the regression analysis. Because the influence of the carbon monoxide mixing ratio requires only addition, multiplication and a minimum of logic, the method can be implemented on very small computers or microprocessors.
Improved geophysical algorithms are shown to be able to determine sea surface temperature (SST) to an accuracy of 1 C (1 sigma) under favorable surface and atmospheric conditions over an SST range of 10-30 C. Under similar conditions, the radiometer wind retrievals track the scatterometer winds within a scatter of 2 m/s (1 sigma) over a wind speed range of 0-25 m/s. These conditions require that contamination from land, rain, sun glint, and radio frequency interference be avoided. What is more, water vapor determinations in the midlatitudes and in the tropical Pacific are found to agree with estimates of precipitable water from radiosondes to within 10%.
Since infrared measurements are only very slightly affected by whitecap and banking angle influences, the combined multifrequency radiometric signatures of the L-band, the S-band, and an infrared radiometer are used in identifying freshwater outflows (submerged and superficial). To separate the river and lagoon outflows from the submarine outflows, geographical maps with a scale of 1:100,000 are used. In all, 44 submarine freshwater springs are identified. This is seen as indicating that the submarine freshwater outflow locations are more numerous around the island than had earlier been estimated. Most of the submarine springs are located at the northwest and southeast portion of the Puerto Rican coastline; the success in detecting the submarine springs during both missions at the northwest portion of the island is 39%. Salinity and temperature distribution plots along the flight path in longitude and latitude coordinates reveal that runoff direction can be determined.
Water-cooled Kendall radiometer measures output of solar energy concentrators. Unit measures irradiance up to 30,000 solar constants with 1 percent accuracy and responds to wavelengths from ultraviolet to far infrared.
To demonstrate the success of utilizing passive microwave sensors in monitoring synoptic scale rainfall, two studies are described in which electrically scanning microwave radiometers (ESMR-5 and 6) on board Nimbus 5 and 6 were employed using a Langrangian frame of reference. The first study suggests a method of utilizing ESMR-5 measurements to quantize rainfall over water within tropical and extratropical storms and to use these measurements to monitor and possibly predict storm intensity. The second study suggests a method of monitoring the coverage and movement of synoptic rain over land by employing ESMR-6.
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.
The development of the cloud indicator index (CII) for use with METSAT's advanced very high resolution radiometer (AVHRR) is described. The CII is very effective at identification of clouds. Also, explored are different solar correction and standard techniques and the impact of these corrections have on the information content of AVHRR data.
Calibration and processing techniques enacted during first year of operation of the Nimbus-7 scanning multichannel microwave radiometer (SMMR) are described. It was found that in-orbit calibration was necessary, as was fine-tuning of the geophysical parameter retrieval parameters to account for anomalies such as lower-than-expected polarization differences in ocean radiances. Phase shifts in the scan angles were corrected in order to avoid polarization mixing. Calibration constants to eliminate cross-talk and phase shift effects were established for radiation reflected from the earth, then averaged over data from 300 orbits to fit points on a sine curve to better than 0.2 K accuracy. An iterative approach was determined to be necessary due to signal anomalies caused by antenna dish oscillations. Global ocean and atmosphere parameters used to construct a radiation model of ten latitude bands are presented for use in radiation transfer equations.