Showing papers on "Radiometer published in 1972"

Radiometer for Remote Sounding of the Upper Atmosphere

Abstract: The pressure-modulated carbon dioxide radiometer is a new kind of instrument capable of making temperature soundings in the 40-80-km region of the earth's atmosphere. It is intended to be mounted on a polar-orbiting satellite, where it will give global coverage of the upper atmosphere in a region that is not well understood at present but that is, as rocket soundings show, clearly the seat of many interesting and vigorous phenomena. The new technique employs a cell containing carbon dioxide as a filter. The pressure and hence transmission of this cell is periodically modulated, resulting in the selection of thermal radiation from the strong lines in the spectrum of atmospheric carbon dioxide. This radiation originates at levels in the atmosphere where the pressure is low. The energy grasp of the device is large enough to give high sensitivity.

Ground-Based Determination of Low Altitude Temperature Profiles by Microwaves

Abstract: Vertical temperature profiles of the lower atmosphere are determined from clear air ground-based measurements of microwave thermal emission by oxygen. Angular emission data from two diverse meteorological locations are mathematically inverted by statistical techniques to recover the vertical profiles. Inversion of 52.5 GHz data, gathered at Upolu Point, Hawaii, Hawaii, resulted in an average root-mean-square (rms) difference of 1.27°K between inverted and radiosonde measured profiles from 0 to 10 km. Pressure and humidity profiles are simultaneously estimated from the data; numerical integration of the inverted humidity profiles results in a determination of total vertical water content with a relative accuracy of about 10 percent. Radiometer emission data at 54.0, 54.5, and 55.0 GHz, taken at Salt Lake City, Utah, are inverted with resulting average rms differences of 1.17°K over the height interval from 0 to 6.4 km. A priori temperature variance, corresponding to known surface conditions, is re...

Radiative heating to the Apollo command module: Engineering prediction and flight measurement

Abstract: The theory and engineering techniques used for the prediction of the Apollo entry thermal-radiation environment are presented. The radiation predictions are shown to be in satisfactory agreement with the Apollo 4, FIRE 1, and FIRE 2 flight radiometer data. The characteristics and performance of the Apollo flight radiometer and ablator-mounted configuration were determined through arc jet simulation tests.

Infrared heterodyne solar radiometry.

Abstract: An infrared heterodyne radiometer has sufficient sensitivity for application to high resolution spectrometric studies of the sun and the absorption of sunlight in the atmosphere. In the 10-micron region, the resolution can typically range from less than .0067/cm to .067/cm. The minimum detectable signal can approach 10 to the -24th power W/Hz. The infrared heterodyne radiometer (IHR) can also be used for atmospheric propagation studies at the emission frequencies of the CO2 laser for the examination of the feasibility of space-to-ground laser communication links.

Dielectric constants of soils at microwave frequencies-2

Abstract: A knowledge of the complex dielectric constant of soils is essential in the interpretation of microwave airborne radiometer data of the earth's surface. Measurements were made at 37 GHz on various soils from the Phoenix, Ariz., area. Extensive data have been obtained for dry soil and soil with water content in the range from 0.6 to 35 percent by dry weight. Measurements were made in a two arm microwave bridge and results were corrected for reflections at the sample interfaces by solution of the parallel dielectric plate problem. The maximum dielectric constants are about a factor of 3 lower than those reported for similar soils at X-band frequencies.

The first year of the selective chopper radiometer on Nimbus 4

Abstract: The selective chopper radiometer, an instrument for the remote measurement of atmospheric temperature from the surface to about 50 km altitude, was launched on the Nimbus-4 satellite in April 1970. The performance of the instrument during its first year of operation is described. Good data have been received throughout this period. Various mean atmospheric cross-sections, temperature profiles and thickness maps are presented as examples of the data which are available from the instrument.

The Radio Continuum of the Large Magellanic Cloud. III. The Sources at 11 cm Wavelength

Abstract: A catalogue is given of radio sources observed in the Large Magellanic Cloud at 11 cm wavelength. A map of the radio brightness in the 30 Doradus region is included. The observations were made with a low-noise correlation radiometer and the Parkes 64 m radio telescope.

Monitoring atmospheric pollutants with a heterodyne radiometer transmitter-receiver

Abstract: The presence of selected atmospheric pollutants can be determined by transmitting an infrared laser beam of proper wavelength through the atmosphere, and detecting the reflections of the transmitted beam with a heterodyne radiometer transmitter-receiver using part of the laser beam as a local oscillator. The particular pollutant and its absorption line strength to be measured are selected by the laser beam wave length. When the round-trip path for the light is known or measured, concentration can be determined. Since pressure (altitude) will affect the shape of the molecular absorption line of a pollutant, tuning the laser through a range of frequencies, which includes a part of the absorption line of the pollutant of interest, yields pollutant altitude data from which the altitude and altitude profile is determined.

A multispectral technique to determine sea surface temperature using Nimbus 2 data.

Abstract: Three channels of the Nimbus 2 five-channel Medium Resolution Infrared Radiometer have been employed in the development of a technique to determine sea surface temperature. Two of the channels in the 0.2-4.0 and 6.4-6.9 micron spectral regions are used to indicate a cloud-free line of sight and the third, a high signal-to-noise window channel (10-11 microns), measures the equivalent blackbody temperature (Tbb) which is a function of the thermal emission from the sea surface and the intervening atmosphere. Equivalent blackbody temperatures and normalized reflectance thresholds were established using frequency distributions from the 6.4-6.9 and 0.2-4.0 micron channels, respectively, to determine the existence of cloud-free conditions. The window Tbb's were compared with ship ocean temperature measurements for a one-month period over the western North Atlantic. This comparison revealed a plus or minus 1.5 K dispersion about the mean difference between the ship temperatures and window Tbb's between 31-34 N.

Dual beam radiometer for clear air turbulence measurement

Abstract: An improved dual beam radiometer comprising radiation detecting means; a source of reference radiation; a rotating chopper for alternately passing radiation from the atmosphere and reflecting radiation from the reference source onto the detecting means; a rotating filter disc having four sectors interposed in the radiation path between the rotating chopper and the detecting means for controlling the wavelength of the radiation applied to the detecting means, the rotating filter disc being operative, synchronously with the rotating chopper, to periodically change the wavelength of the atmospheric radiation and the wavelength of the reference radiation applied to the detecting means; and means for controlling the temperature of the reference source as a function of atmospheric temperature adjacent to the radiometer.

Meteorological applications of the Nimbus 4 Temperature-Humidity Infrared Radiometer, 6.7 micron channel data

Abstract: Mid-tropospheric circulation features under essentially clear sky conditions have been noted in the data of the 6.7 μm channel of the Nimbus 4 Temperature-Humidity Infrared Radiometer (THIR) while at the same time these features were undetected by the 11.5 μm channel of the same instrument. The characteristic response of the 6.7 μm channel to atmospheric water vapor emission is primarily from the 250-mb (10.5 km) to 500-mb (5.5 km) levels with a peak contribution at 350 mb (8 km). Dry and moist patterns seen in the 6.7 μm data on 21 February 1971 have been integrated into a 400-mb moisture analysis over the United States. This analysis provided more detailed and timely information than was conventionally available about the advection of dry air aloft prior to development of the Mississippi Tornado of February 1971. The derivation of middle to upper atmosphere flow patterns from the Nimbus 4 THIR, 6.7 μm data under cloud-free conditions has a direct application on a global scale for the GARP and W...

Ground-Based Sensing of Temperature Profiles from Angular and Multi-Spectral Microwave Emission Measurements

Abstract: The use of angular-scan and multi-spectral techniques for Inferring temperature profiles from ground-based radiometric observations of emission by atmospheric oxygen is discussed. A recently developed multi-frequency radiometer used to evaluate, experimentally, the two techniques is described. Temperature profiles inferred from emission measurements are compared to radiosonde profiles recorded simultaneously with the radiometric data. It is concluded that a combination of angular-scan and multi-spectral input data yields a more accurate profile recovery than other sets of input data.

Development of a satellite microwave radiometer to sense the surface temperature of the world oceans

Abstract: A proposed S-band radiometer for determining the ocean surface temperature with an absolute accuracy of + or - 1 Kelvin and a resolution of + or - .1 Kelvin was placed under the Advanced Applications Flight Experiment for further development into Nimbus readiness state. The results of assessing the following are described: effects due to the state of the sea surface, effects caused by the intervening atmosphere, and effects associated with imperfections in the instrument itself. An extensive sea truth program is also described for correlation of aircraft test flight measurements or of satellite remote measurement to in-situ data. An improved radiometer design is a modified Dicke-switch type with temperature stabilized, microwave integrated circuit, front-end and with a pulsed injection-noise nulling system. The radiometer has a multimode rectangular horn antenna with very low ohmic losses and a beam efficiency of 98% or better.

Experimental Comparisons of the International Pyrheliometric Scale with the Absolute Radiation Scale

Abstract: Solar irradiance measurements by instruments (Eppley Angstrom Pyrheliometers) reproducing the International Pyrheliometric Scale (IPS) have been compared with measurements made simultaneously by a number of JPL Active Cavity Radiometers (ACR) and the Practical Absolute Cavity Radiometer (PACRAD). The results of these tests demonstrate a systematic difference between the absolute radiation scale as defined by the ACR and PACRAD measurements and the IPS.

Infrared Radiometry Experiment on Mariner 9

Abstract: The brightness temperatures at 10 and 20 micrometers measured by the Mariner 9 infrared radiometer differ substantially from those predicted by the radiometer results of Mariners 6 and 7. The results indicate a significant latitude-dependent contribution of the atmospheric dust to the observed thermal emission.

A multispectral cloud type identification method using Nimbus 3 MRIR measurements.

Abstract: Using Nimbus 3 medium resolution infrared radiometer measurements, a multispectral cloud type identification method is developed. This method includes a fourth spectral region (20-23 microns), the use of radiative transfer theory, and a semiquantitative evaluation of satellite cloud type estimates with concurrent high resolution photography from aircraft flights.

Direct determination of the thickness of stratospheric layers from single-channel satellite radiance measurements.

Abstract: The direct use of measured radiances for determining the thickness of stratospheric layers is investigated. Layers based at 100-10 mb, with upper boundaries at 10-0.5 mb, are investigated using a carefully selected family of stratospheric temperature profiles and computed radiances. On the basis of physical reasoning, a high correlation of thickness with radiance is anticipated for deep layers, such as the 100- to 2-mb layer (from about 15 to 43 km), that emit a substantial part of the infrared energy reaching a satellite radiometer in a particular channel. Empirical regression curves relating thickness and radiance are developed and are compared with blackbody curves obtained by substituting the blackbody temperature in the hydrostatic equation. Maximum thickness-radiance correlation is found, for each infrared channel, for the layer having the best agreement of empirical and blackbody curves.

Dual color radiometer method selectively discriminating against a radiant energy emissivity characteristic of a preselected atmospheric state

Abstract: A dual color radiometer method for detection and discrimination of radiant energy emissivity characteristics of preselected atmospheric states. The dual output signals from the radiometer and corresponding to a respective first and second atmospheric spectral sample in a preselected spectral region, are differentially combined, one of the spectral sample signals being compensatorily gain changed such that the component signal intensity in both such output signals for a preselected atmospheric state are equal. Thus, the differentially combined signals provide a resultant signal indicative of an atmospheric state other than such preselected atmospheric state.

A radiometer‐sonde for observing stratospheric emission due to water vapour in its rotational band

Abstract: A balloon-borne instrument is described which measures the downward flux from atmospheric water vapour in the 20–60 μm region. The instrument uses a thermistor bolometer as the infra-red sensor. A special infra-red filter composed of beryllium oxide embedded in polyethylene provides the desired optical characteristics for the instrument. In-flight energy calibration is carried out with two reference black bodies. The radiometer-sonde is flown in conjunction with a conventional radiosonde, which provides atmospheric temperature, and pressure data for the ascent. Results have been obtained from 3 ascents. In the stratosphere the observed flux is consistent with the flux calculated for a water vapour mixing ratio of 2 × 10−6, and using published spectral data. The divergence of the flux corresponds to cooling at a rate of 0.4°C/day.

Compensation means for ambient temperature changes of a radiation chopper in a radiometer

Abstract: A radiometer is provided with optics, a reference black body cavity, a radiation detector located at the apex of the black body cavity, a radiation chopper external to the black body cavity having alternate mirrored and open segments, and conventional electronic processing circuitry for receiving and processing an output signal from the radiation detector. A blackened vane is positioned in close proximity to the chopper for tracking the temperature of the radiation chopper, and extends into the field of view of the radiometer on the occurrence of an open sector of the chopper, with the area of the vane which extends into the field of view of the radiometer being equal to the clear aperture area of the optical means times the emissivity of the radiation chopper, which provides compensation for changes in the radiation chopper temperature.

Microwave Noise Standards in the United Kingdom

Abstract: This paper outlines the work currently being carried out at the Royal Radar Establishment (RRE) in the RF and Microwave National Standards Division of the British Calibration Service, on both hot and cold noise standards and comparator systems. The design of three cryogenic noise sources for use in WG15 are described in detail along with the theoretical calculation of their output noise power spectral density. A noise-adding radiometer is analyzed, and finally the sources of uncertainty involved in a recent calibration are discussed.

The radiation budget of the earth-atmosphere system as measured from the Nimbus 3 satellite /1969-1970/.

Abstract: Data from the Medium Resolution Infrared Radiometer (MRIR) experiment on Nimbus 3 have provided global radiance measurements during four seasons (April 1969-February 1970). From these data, values of the total radiation budget of the earth-atmosphere system were derived on varying time and space scales and were compared with previous satellite measurements and theoretical computations. Results confirm earlier satellite measurements. They show a warmer and darker planet than was previously believed. In addition, the Nimbus 3 data offer the first medium resolution views of both the Northern and Southern Hemispheres' radiation budgets during all seasons.

Three Optical Methods for Remotely Measuring Aerosol Size Distributions

Abstract: Three optical probing methods for remotely measuring atmospheric aerosol size distributions are discussed and contrasted. The particular detection methods which are considered make use of monostatic lidar (laser radar), bistatic lidar, and solar radiometer sensing techniques. The theory of each of these measurement techniques is discussed briefly, and the necessary constraints which must be applied to obtain aerosol size distribution information from such measurements are pointed out. Theoretical and/or experimental results are also presented which demonstrate the utility of the three proposed probing methods.

Radiometric Measurements of Temperature Profiles in the Planetary Boundary Layer

Abstract: A ground-based 5-mm wavelength radiometer, named the Radiometric Thermasonde, has been developed. Typical vertical temperature profiles, derived from a recently developed radiometric data processing technique, are compared with profiles measured simultaneously by conventional techniques. Two years of performance testing of the operational prototype Thermasonde have demonstrated the feasibility of using radiometric remote probing techniques to describe thermal stability conditions within the first 1.5–2.0 km above the surface, during fair weather conditions. Preliminary tests indicate that temperature profiles derived from the Thermasonde can provide useful information, particularly for air pollution meteorology, for describing dispersion characteristics within the planetary boundary layer. The evaluation of a preliminary data reduction technique is described.

Nimbus limb radiometer, apollo fine sun sensor, and skylab multispectral scanner.

Abstract: Examples of three different types of electrooptical systems developed by the Honeywell Radiation Center for NASA are described. One is a multichannel infrared (~15 μρ radiometer that will permit temperature and constituent inferences over the globe; it carries a one-year supply of cryogenics for the trimetal infrared detectors. The second is the Apollo telescope mount fine sun sensor, a tracking device making use of solar radiation and the transmission near critical angle of refraction, that will track within ±2 sec of arc to a designated point on the sun. The final example is the Skylab S-192 multispectral (thirteen channels from 0.4 μ to 12 μρ mapper for a variety of earth resources applications.

Rapid variations of sea surface temperature in the persian gulf as recorded by nimbus 2 hrir

Abstract: Nimbus 2 high resolution infrared radiometer (HRIR) observations over the Persian Gulf have been analyzed for cloud-free nights from June to November 1966. The spatial distribution of sea surface temperatures as observed by the satellite radiometer responded to the prevailing surface winds. Satellite radiometric observations can be used to locate large-scale air—sea interaction features.

Fundamental principles of absolute radiometry and the philosophy of this NBS program (1968 to 1971)

Abstract: A description is given work performed on a program to develop an electrically calibrated detector (also called absolute radiometer, absolute detector, and electrically calibrated radiometer) that could be used to realize, maintain, and transfer a scale of total irradiance. The program includes a comprehensive investigation of the theoretical basis of absolute detector radiometry, as well as the design and construction of a number of detectors. A theoretical analysis of the sources of error is also included.

A Technique for Measuring Spectral Emittance

Abstract: A radiometer system is described which allows one to measure directly the spectral emittance of both solid and powdered surfaces. The data logging is automated by interfacing a spectrophotometer with a minicomputer system.