Showing papers on "Radiometer published in 1985"
TL;DR: In this article, a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant power measurements, is described.
Abstract: The adoption in 1979 of a new definition of the candela, which permitted a detector-based approach to the realization of the unit, has emphasized the importance of high-accuracy absolute radiation detectors. This paper describes a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant-power measurements. The principal advantages of operating the radiometer at liquid helium temperatures are that the detector can be a large, highly absorbing cavity (absorptivity 99.998%) and that exact equivalence of electrical and radiant heating can be clearly demonstrated. It will be the primary absolute detector for a new realization of the candela at NPL and will provide the basis for the development of a wider range of radiometric and spectroradiometric standards. The use of the radiometer to measure the radiant power of an intensity-stabilized laser source at the milliwatt level with an uncertainty of 4 parts in 105 is also described, together with its application in the determination of the responsivity of transfer-standard detectors, such as silicon photodiodes.
248 citations
TL;DR: A detailed analysis of the calibration procedures for the NOAA advanced very high resolution radiometer (AVHRR) based on thermal vacuum test data was performed as part of the Warm Core Rings Experiment as discussed by the authors.
Abstract: A detailed analysis of the calibration procedures for the NOAA advanced very high resolution radiometer (AVHRR) based on thermal vacuum test data was performed as part of the Warm Core Rings Experiment. We find systematic differences in the derived calibration results and those reported in the various addenda to work by Lauritson et al. (1979). A weak, but important, dependence in calibration upon internal operating temperature is also observed. Calibration results for various AVHRR radiometers show instrument specific changes in the relative emittance between internal and external calibration targets. A consistent calibration methodology is developed based on this analysis of the thermal vacuum test data. Use of these new results provides an improvement of radiometer calibration at the ±0.2°C level. Such an improvement is quite important to the absolute accuracy of surface thermal fields which are derived from these data utilizing various multichannel atmospheric water vapor correction schemes. Demonstration of such accuracies with presently operational sensors is of importance to climate related studies being planned for the next decade since it shows that appropriate processing can lead to higher-quality SST fields.
136 citations
TL;DR: In this paper, the microwave radiometric measurements made by the Skylab 1.4 GHz and by the 6.6 GHz and 10.7 GHz channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer were analyzed to study the large-area soil moisture variations of land surfaces.
106 citations
TL;DR: In this article, a method is described whereby net radiation is evaluated by combining ground-based meteorological and remote multispectral measurements, which can be used to construct a net radiation map of relatively large areas.
81 citations
TL;DR: In this article, an infrared radiative transfer model was used to derive cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths.
Abstract: Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes. The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.
76 citations
TL;DR: In this article, an algorithm is developed which uses two microwave radiometer channels to estimate quantitative fractions of first-year and multi-year sea ice types, applied to data obtained from satellite sensors, and the data trends are used to refine values of the emissivities.
Abstract: An algorithm is developed which uses two microwave radiometer channels to estimate quantitative fractions of first-year and multiyear sea ice types. The algorithm is applied to data obtained from satellite sensors, and the data trends are used to refine values of the emissivities. The algorithm was tested, and results were in reasonable agreement with visual observations, where mixtures of first-year sea ice and multiyear sea ice were known to coexist. However, on a synoptic basis the satellite estimates differ from visual and radar means of classifying ice that has survived at least one melt season (old ice). A possible explanation for the discrepancy is that the emissivity of sea ice changes over time periods longer than one melt season.
74 citations
TL;DR: In this paper, a C band radiometer and an X band scatterometer were used to collect both active and passive microwave remote sensing data over Greenland with the NASA C-130 aircraft used as a platform.
Abstract: Microwave remote sensing measurements were collected over Greenland with the NASA C-130 aircraft used as a platform. The principal instruments were a C band radiometer and an X band scatterometer, which simultaneously collected both active and passive microwave remote sensing data. The results indicate that subsurface inhomogeneities control the scattering and emission process, including anisotropic effects. The results strongly suggest that microwave remote sensing techniques can provide a relative measure of the density and orientation of the volume scatters.
45 citations
TL;DR: In this paper, a water-vapor radiometer is developed to determine atmospheric path-delay corrections for geodynamics applications, and the performance objective is the determination of the line-of-sight path delay though the atmosphere due to water vapor with a one-sigma error less than 0.5 cm at the zenith.
Abstract: A new water-vapor radiometer is being developed to determine atmospheric path-delay corrections for geodynamics applications. The radiometer has microwave channels at 20.7, 22.2, and 31.4 GHz, and includes new features which should promote radiometric precision while at the same time reduce instrument complexity. The instrument will be compact, portable, and will possess a self-diagnostic capability to ensure reliability. The performance objective is the determination of the line-of-sight path delay though the atmosphere due to water vapor with a one-sigma error less than 0.5 cm at the zenith.
42 citations
Patent•
26 Apr 1985
TL;DR: In this paper, a microwave radiometer reconstructs images by fanbeam inversion using a fanbeam antenna and a computer, and the scene is reconstructed by the computer using an inverse Radon transform, which compensates for the conicity of scanning fanbeams.
Abstract: A microwave radiometer reconstructs images by fanbeam inversion. True time delay (100), frequency (600, 700) and mechanical scanning systems (200) are disclosed. The mechanically scanning radiometer includes a fanbeam antenna (210) to scan a scene so that the antenna output is a projection of the scene taken along the direction of scan. The mechanical scanning motion is provided by a rocking motor (254) controlled by a computer (214). Projections are obtained for successive orientations as the antenna is rotated by another motor (212). By application of an inverse Radon transform, the scene scanned is reconstructed by the computer. In one frequency scanning system (600), a filter bank spectrometer is implemented to obain the projections, and in the other frequency scanning system (700), a transform spectrometer implemented. In the delay scanning system (100), a beam forming computer is used in the reconstruction process. A modification of the Radon transform is disclosed which compensates for the conicity of electronically scanning fanbeams.
38 citations
01 Aug 1985
TL;DR: In this paper, the authors describe the Stanford E L F /V L F noise m easurem ent project, including the instrum enta tion comprising each of the radiometers, the form of the ir analog and digital m affurem ents (which are made under the control of a minicomputer), and the d a ta processing techniques th a t will be used.
Abstract: S tanford University is currently conducting a global survey of electromagnetic noise in the 10 32,000 Hz (ELF/V LF) frequency band using a network of eight computer-controlled receiving systems, or ‘radiom eters.’ One goal of this m easurem ent program is to improve communication in the E L F/V L F band by providing more upto-date and complete inform ation about the properties of E L F/V L F noise (both na tu ra l and man-made) than is currently available—the last extensive survey of noise in the same frequency band was made over two decades ago. In this p resentation we describe the Stanford E L F /V L F noise m easurem ent project, including the instrum enta tion comprising each of the radiometers, the form of the ir analog and digital m easurem ents (which are made under the control of a minicomputer), and the d a ta processing techniques th a t will be used. T he results of previous noise surveys are briefly reviewed and the significance of the overall decline of noise power with increasing frequency revealed by these surveys and other studies is discussed in the context of the scientific applications of the noise d a ta obtained by the radiom eter network.
38 citations
TL;DR: The Along Track Scanning Radiometer (ATSR) is a planned ERS-1 payload for accurate sea-surface temperature measurements under two different incidence angles from a conical scan.
Abstract: The Along-Track Scanning Radiometer (ATSR) is a planned ERS-1 payload for accurate sea-surface temperature measurements under two different incidence angles from a conical scan. It is investigated whether it can additionally be used for cloud stereoscopy and wind determinations as proposed by DFVLR for the Stereo Line Scanner (SLS). Although not designed for these types of measurements the ATSR seems very useful for a pilot experiment with only a lower resolution than proposed for the SLS. Because of distortions that occur with the conical scan of the ATSR, synthetic stereo imaging with additional height corrections is recommended instead of direct stereoscopy. Quantitative cloud heights can be derived from parallax measurements. Estimations of the influence of the pixel size and the alignment changes lead to cloud-height accuracies of up to ±750m. The influence of cloud motion on the parallax may be corrected with cloud-motion vectors derived from geosynchronous satellite data. An experiment for...
TL;DR: In this paper, the authors estimate the feasibility of monitoring the surface temperature of an active volcano using satellite thermal infrared data, using a Digital Terrain Model (DTM) to correct for the variations of mean ground temperature and atmospheric absorption with altitude.
TL;DR: In this article, the effect of detector temperature on the voltage output from silicon (Si) and lead sulfide (PbS) detectors of a multiband spectral radiometer was evaluated.
TL;DR: In this paper, an eight-channel radiometer for simultaneous measurement of electron temperatures at different radii via electron cyclotron emission is described, which is divided into two parts, the interchangeable front end and the filter section.
Abstract: An eight‐channel radiometer for simultaneous measurement of electron temperatures at different radii via electron cyclotron emission is described. It is divided into two parts, the interchangeable front end and the filter section. By replacing the front end, both first and second‐harmonic electron cyclotron emission measurements are possible in the range of 50–180 GHz. The instrument is absolutely calibrated with an accuracy estimated to be within ±10%. The spatial resolution ΔR/R is of the order 10−3, the temporal resolution 20 μs.
01 Jan 1985
TL;DR: A prototype pushbroom microwave radiometer developed at NASA's Langley Research Center is described in this article, which is a multibeam L-band (1413 MHz) radiometer system providing simultaneous cross track measurements.
Abstract: A method is described for providing soil moisture measurements from satellites by performing simultaneous measurements across track (the pushbroom approach). The method has the advantage of obtaining the required swath width without sacrificing sensitivity. A prototype Pushbroom Microwave Radiometer developed at NASA's Langley Research Center is described. It is a multibeam L-Band (1413 MHz) radiometer system providing simultaneous cross track measurements. Results of flight tests onboard a P-3 aircraft are discussed.
TL;DR: Two activities, (1) orbit prediction correction using optical observation and (2) detection of the earth laser beacon by the radiometer, are described.
Abstract: Some experimental results for detection of a ground-based laser beacon by a geosynchronous satellite are reported. A 50-cm diam telescope and silicon intensifier tube camera were used for optical observation of the satellite. The transmitted argon laser beam was detected by the visible channel of a radiometer on board the Japanese Geostationary Meteorological Satellite. Two activities, (1) orbit prediction correction using optical observation and (2) detection of the earth laser beacon by the radiometer, are described.
01 Jun 1985
TL;DR: In this article, a NASA flight experiment is described that provides an opportunity to obtain a large base of radiometric data for high-altitude, high-velocity thermochemically nonequilibrated-flow conditions.
Abstract: A forthcoming NASA flight experiment is described that provides an opportunity to obtain a large base of radiometric data for high-altitude, high-velocity thermochemically nonequilibrated-flow conditions. As a preliminary to the design of a radiometer for this experiment, an approximate method for predicting both equilibrium and nonequilibrium radiative surface fluxes is described. Spectral results for one trajectory state, a velocity of 10 km/sec at an altitude of 85 km, are presented. These results are then used to develop some of the instrument parameters that will be needed for designing of the three genre of radiometers that are proposed for this experiment.
Patent•
03 Dec 1985
TL;DR: In this article, the surface emissivity of a mesh membrane material is determined by a radiometer attached to a horn antenna, a test section sealed to the horn antenna and a matched load exposed to the interior of the system.
Abstract: The invention embodies a system and procedure for independently determining the surface emissivity of a mesh membrane material 12. The system is a closed one with respect to unwanted or uncorrected radiation outside the system and is composed of a radiometer 11 connected to a horn antenna 13, a test section 15 sealed to the horn antenna 13 and a cryogenically cooled matched load 17 exposed to the interior of the system. The material 12 is enclosed in a convection test chamber 14 within test section 15, heated within test chamber 14 and allowed to radiate within the system such that a component of the radiation energy of material 12 is measured by the radiometer 11 in terms of brightness temperature. The matched load 17 serves as the stabilizing source of uncorrelated radiation within the system by radiating within the system at a constant cryogenic temperature. The actual physical temperature of the material 12 is also measured during the heating process. The difference in brightness temperature over a selected period of time when divided by the physical temperature over the same period of time is the emissivity of the material 12 according to a derivation of the Raleigh-Jeans approximation for an ideal system free from all uncorrelated radiation.
TL;DR: In this article, a continuous comparison radiometer has been implemented at 97 GHz using quasi-optical techniques for local oscillator injection and realization of a 90° hybrid with Schottky-diode mixers and FET amplifiers.
Abstract: A continuous comparison radiometer has been implemented at 97 GHz using quasi-optical techniques for local oscillator (LO) injection and realization of a 90° hybrid. Cryogenically cooled Schottky-diode mixers and FET amplifiers give a double-sideband (DSB) system temperature of 250 K. The system is self-calibrating and optimized under computer control. The root-mean-square (rms) fluctuations due to the receiver are less than 0.025 K with a 1-s integration time.
TL;DR: The performance of a ground-based microwave radiometer of new design to be used for remote sensing of the temperature profile of the atmosphere has been tested in this article, where the radiometer measurements have been analyzed with the statistical inversion method and the retrieved profiles have been compared with 28 simultaneous radiosoundings.
Abstract: The performance of a ground-based microwave radiometer of new design to be used for remote sensing of the temperature profile of the atmosphere has been tested. It is continuously tunable in the range 52-8-58-8 GHz and has a high absolute accuracy. The radiometer measurements have been analysed with the statistical inversion method and the retrieved profiles have been compared with 28 simultaneous radiosoundings. The r.m.s. difference under clear-sky and cloudy conditions was, on these occasions, less than l-5degK up to 6km and 4km, respectively, less than OdegK up to 8 and 5-5 km, respectively, and less than 3-0degK up to 9 and 7-5 km, respectively. Methods to increase the profiling accuracy are discussed.
01 Jan 1985
TL;DR: In this paper, an analysis of the magnitude and variability of the effect of the atmosphere on high-altitude Daedalus Airborne Thematic Mapper data is presented, by regressing ATM radiances against ground radiances (from measurements by a helicopter-mounted Barnes Modular Multiband Radiometer).
Abstract: An analysis is presented of the magnitude and variability of the effect of the atmosphere on high-altitude Daedalus Airborne Thematic Mapper data. By regressing ATM radiances against ground radiances (from measurements by a helicopter-mounted Barnes Modular Multiband Radiometer), it was possible to account for atmospheric conditions and variability across a 250 km transect in Oregon to estimate coniferous forest leaf area index. The technique permitted scene contrast to be increased, providing an improved capability for measurement of ground feature radiance.
TL;DR: In this paper, the results of one such experiment, utilising a 12 GHz radiometer, in Hong Kong were reported, which showed that rain attenuation is a significant factor in determining the operating margins of communications satellite systems, particularly for links to tropical, high-rainfall-rate regions.
Abstract: At frequencies above 10 GHz, rain attenuation can be a significant factor in determining the operating margins of communications satellite systems, particularly for links to tropical, high-rainfall-rate regions. To establish accurate prediction models for those regions, it is necessary to conduct a number of measurements. The letter reports the results of one such experiment, utilising a 12 GHz radiometer, in Hong Kong.
TL;DR: In this paper, a treatment of WVR data is proposed and evaluated to reduce the effect of systematic WVR systematic errors by estimating parameters that specify an assumed functional form for the error.
Abstract: The water-vapor radiometer (WVR) is used to calibrate unpredictable delays in the wet component of the troposphere in geodetic microwave techniques such as very-long-baseline interferometry (VLBI) and Global Positioning System (GPS) tracking. Based on experience with Jet Propulsion Laboratory (JPL) instruments, the current level of accuracy in wet-troposphere calibration limits the accuracy of local vertical measurements to 5-10 cm. The goal for the near future is 1-3 cm. Although the WVR is currently the best calibration method, many instruments are prone to systematic error. In this paper, a treatment of WVR data is proposed and evaluated. This treatment reduces the effect of WVR systematic errors by estimating parameters that specify an assumed functional form for the error. We evaluate the assumed form by comparing the results of two similar WVR's operating near each other. Finally, we estimate the observability of the error parameters by covariance analysis.
TL;DR: In this article, the improved spatial and thermal resolution of a broadband microwave correlation radiometer is discussed and upper and lower bounds of the combined spatial and temperature resolution in a dense transmission medium are presented along with data obtained for two thermal sources in air.
Abstract: The improved spatial and thermal resolution of a broad-band microwave correlation radiometer is discussed. Theoretical upper and lower bounds of the combined spatial and thermal resolution in a dense transmission medium are presented along with data obtained for two thermal sources in air. The application of broad-band correlation techniques to medical microwave thermography is novel, and the results indicate that electronic scanning of tissue should be possible.
TL;DR: In this article, a new method was developed for measuring weak absorption in bulk materials and coatings based on recording a change in the integrated thermal radiation flux from the surfaces of samples heated by periodic laser radiation pulses.
Abstract: A new method was developed for measuring weak absorption in bulk materials and coatings It is based on recording a change in the integrated thermal radiation flux from the surfaces of samples heated by periodic laser radiation pulses The possibility is discussed of making absolute measurements by simulation of surface heat sources in the materials investigated, and also by comparing them with standard samples The sensitivity of the method is estimated and the results of absorption measurements on a number of materials are presented Consideration is given to limitations imposed on the operating range of laser pulse repetition frequencies by the thickness of the layer of the substance emitting the thermal flux and by the increase in the transverse dimensions of the illuminated area arising on account of thermal diffusion
TL;DR: In this article, the retrieval procedure of liquid water content (LWC) in cloud or rainfall distribution by a combination of microwave radiometry and radar and its numerical simulation is described, and the performance of a combined dual-wavelength (35.0 and 9.375 GHz) radar-radiometer system for the remote sensing of cloud LWC and rainfall is given.
Abstract: This paper describes the retrieval procedure of liquid water content (LWC) in cloud or rainfall distribution by a combination of microwave radiometry and radar and its numerical simulation. The performance of a combined dual-wavelength (35.0 & 9.375 GHz) radar-radiometer system for the remote sensing of cloud LWC and rainfall is given. During the two summers of 1980 and 1981, the preliminary observations of different clouds and storms by the combined system and combined radar-radiometric cloud and rain parameter retrievals are carried out. Research results show that by the use of the combined radarradiometric method, improvement are obtained in accuracy of rms LWC and rainfall over the pure radiometric technique or the radar alone.
Patent•
20 Dec 1985
TL;DR: In this article, the authors used a servo system to orient the scan mirror of the radiometer into the path of a sufficiently bright star such that motion of the satellite will cause the star's light to impinge on the scan mirrors and then the visible light detectors.
Abstract: A method and apparatus for determining the orientation of the optical axis of radiometer instruments mounted on a satellite involves a star sensing technique. The technique makes use of a servo system to orient the scan mirror of the radiometer into the path of a sufficiently bright star such that motion of the satellite will cause the star's light to impinge on the scan mirror and then the visible light detectors of the radiometer. The light impinging on the detectors is converted to an electronic signal whereby, knowing the position of the star relative to appropriate earth coordinates and the time of transition of the star image through the detector array, the orientation of the optical axis of the instrument relative to earth coordinates can be accurately determined.
TL;DR: In this paper, a simple obscurer is used to shadow an upward facing radiometer from the direct beam, and the fraction of diffuse flux obscured by the device is calculated from the estimated scattering properties of the atmosphere.
TL;DR: In this article, the authors used the equation of radiative transfer to relate the antenna temperature to the rain rate profile inferred by the airborne microwave radiometer, and the influence of the ocean surface temperature on the radiometer measurements of rain is evaluated by model computation.
Abstract: Data on the airborne microwave radiometer, which is one of the sensors of the airborne microwave rain-scatterometer/radiometer (AMRS) system, are analyzed to infer path-integrated rain rate measured from topside. The equation of radiative transfer is used to relate quantitatively the antenna temperature to the rain rate profile inferred by the scatterometer. The influence of the ocean surface temperature on the radiometer measurements of rain is evaluated by a model computation. The theoretical prediction agrees excellently with the measurements. The effect of nonuniform rain along the propagation path is also evaluated by using the experimental data. It is shown that the excess antenna temperature (difference between the antenna temperature under raining and no-rain conditions) in the 10 GHz band is proportional to the path-integrated rain rate, and a method for determining the reference temperature (antenna temperature under a no-rain condition) is suggested.