Showing papers on "Radiometer published in 1973"
TL;DR: In this article, a multiple wavelength solar radiometer designed for the purpose of measuring atmospheric optical depth at discrete wavelengths through the visible region is described, and the influence of the aerosol size distribution on optical depth is investigated.
Abstract: A multiple wavelength solar radiometer designed for the purpose of measuring atmospheric optical depth at discrete wavelengths through the visible region is described. Experimental techniques, including sample observations, are presented for obtaining atmospheric optical depth from radiometer measurements. These techniques apply for conditions where the optical depth is either temporally variant or invariant during the course of a day. The influence of the aerosol size distribution on optical depth is investigated. Theoretical calculations of the wavelength dependency of the aerosol optical depth contribution are presented for several representative aerosol size distributions. Methods are also presented for estimating the aerosol size distribution and aerosol mass loading from multiwavelength optical depth measurements.
286 citations
TL;DR: In this article, preliminary 10- and 20-μm brightness temperatures of Mars were obtained from the Mariner 6 and 7 radiometers, although the temperatures, on the average, were cooler and shifted with respect to the Martian day during the dust storm.
Abstract: Preliminary 10- and 20-μm brightness temperatures of Mars are presented. More than 35% of the Martian surface was observed with a resolution better than 100 km. On the whole, the results confirm the thermal properties derived from the Mariner 6 and 7 radiometers, although the temperatures, on the average, were cooler and shifted with respect to the Martian day during the dust storm. Thermal inertias and radiometric albedos were derived for many areas; no clear correlation exists between these properties. Thermal structure again was found at the spatial limit of the radiometer; no cases were found in which it was necessary to invoke internal heat sources.
196 citations
TL;DR: In this article, the first time high-resolution data on the earth's annual global radiation budget was provided by the meteorological satellite Nimbus 3 during 10 semi-monthly periods (April-15 August, 3-17 October, 1969; 21 January-3 February, 1970).
Abstract: Measurements of reflected solar radiation and emitted thermal radiation taken with a radiometer on the meteorological satellite Nimbus 3 during 10 semi-monthly periods (April-15 August, 3-17 October, 1969; 21 January-3 February, 1970) provided for the first time high-resolution data on the earth's annual global radiation budget. Results on the planetary albedo, the amount of absorbed solar radiation, the infrared radiation loss to space, and the radiation balance of the earth-atmosphere system are discussed at various scales: global, hemispherical, and zonal averages; as well as global and polar maps with a spatial resolution of about synoptic scale.
182 citations
TL;DR: In this article, the authors described the instrumentation of a probe designed for atmospheric studies on other planets and designated as PAET, which was launched on June 20, 1971, near Bermuda in a trial experiment for measurements of the structure and composition of the terrestrial atmosphere.
71 citations
TL;DR: In this article, an error analysis is carried out on the quasi-equilibrium equation to determine the uncertainties of active cavity radiometer measurements relative to the absolute radiation scale, and the uncertainty of ACR measurements as a function of irradiance level is presented in graphical form.
Abstract: The active cavity radiometer (ACR) is a pyrheliometer that accurately defines the absolute radiation scale. The physics of the pyrheliometric method and the ACR approach to this method are presented in detail. A mathematical abstraction of the method is generated through a quasi-equilibrium analysis of the power balance of the ACR's cavity detector. An error analysis is carried out on the quasi-equilibrium equation to determine the uncertainties of ACR measurements relative to the absolute radiation scale. The uncertainty of ACR measurements as a function of irradiance level is presented in graphical form.
58 citations
56 citations
TL;DR: In this paper, the effects of atmosphere state, nadir angle, cloud amount, cloud height, and random noise on ocean surface temperature sensing from the NOAA series satellites were investigated.
Abstract: Investigation of the effects of atmosphere state, nadir angle, cloud amount, cloud height, and random noise on ocean surface temperature sensing from the NOAA series satellites. The results obtained include the finding that a 10% cloud cover can introduce errors that range from 0.5 K to 4 K depending on cumuloform cloud height, which makes necessary a complete cloud elimination in the analysis. A correction scheme for cloud-free conditions is developed that is essentially free of bias.
44 citations
TL;DR: In this article, a heterodyne radiometer operating in the 9 to 11μm wavelength region was used to detect SO2 and CO2 in the laboratory with sensitivity adequate for remote stack monitoring and other sensing applications.
Abstract: A heterodyne radiometer, operating in the 9‐ to 11‐μm wavelength region, has been used to detect SO2 and CO2 in the laboratory with sensitivity adequate for remote stack monitoring and other sensing applications. CO2 lasers were used as local oscillators. The mixer was copper‐doped germanium, compensated with antimony donors, and the i.f. bandwidth was 500 MHz. Wavelengths of operation were chosen to minimize interference from water vapor.
34 citations
TL;DR: In this paper, measurements from ground level of 53 GHz radiation from molecular oxygen in the stratosphere, using a very precise radiometer, can be used to give stratospheric temperatures.
Abstract: Measurements from ground level of 53 GHz radiation from molecular oxygen in the stratosphere, using a very precise radiometer, can be used to give stratospheric temperatures.
33 citations
TL;DR: In this paper, a determination of the composition of the earth's atmosphere obtained from onboard radiometer measurements of the spectra emitted from the bow shock layer of a high-speed entry probe is reported.
Abstract: A determination of the composition of the earth's atmosphere obtained from onboard radiometer measurements of the spectra emitted from the bow shock layer of a high-speed entry probe is reported. The N2, O2, CO2, and noble gas concentrations in the earth's atmosphere were determined to good accuracy by this technique. The results demonstrate unequivocally the feasibility of determining the composition of an unknown planetary atmosphere by means of a multichannel radiometer viewing optical emission from the heated atmospheric gases in the region between the bow shock wave and the vehicle surface. The spectral locations in this experiment were preselected to enable the observation of CN violet, N2(+) first negative and atomic oxygen emission at 3870, 3910, and 7775 A, respectively. The atmospheric gases were heated and compressed by the shock wave to a peak temperature of about 6100 K and a corresponding pressure of 0.4 atm. Complete descriptions of the data analysis technique and the onboard radiometer and its calibration are given.
25 citations
TL;DR: In this paper, a liquid-helium-cooled radiometer was used to make direct measurements of the background radiation in the spectral range from 1 to 20 cm, and evaluation of the results of two balloon flights performed with the aid of this radiometer.
Abstract: Description of a balloon-borne radiometer designed to make direct measurements of the background radiation in the spectral range from 1 to 20 cm, and evaluation of the results of two balloon flights performed with the aid of this radiometer. Measurements in five different passbands in the spectral region below 20 per cm were made with a liquid-helium-cooled radiometer in two flights at approximately 40-km altitude. The results obtained are found to be consistent with a 2.7 K thermal radiation background. In addition, an atmospheric radiation of certain magnitude is found to dominate the region above 11 per cm.
TL;DR: In this paper, a tethered balloon borne radiometer was used to study the spectral continuum within the 8-13 μm atmospheric window, while simultaneous measurements of temperature and humidity profiles were made.
Abstract: The spectral continuum within the 8–13 μm atmospheric window was studied using a tethered balloon borne radiometer, while simultaneous measurements of temperature and humidity profiles were made. Aerosol absorption was estimated as negligible as the measurements were made in conditions of high visual range. The results from a range of situations were tested separately against a line wing continuum model and a water dimer continuum model, both with appropriate spectral line band models. These results were found to agree well with laboratory data for the dimer model.
TL;DR: It is shown that a laser heterodyne radiometer can be used to measure accurately the atmospheric transmission for laser radiation propagating through the entire atmosphere and the spectral bandwidth must be small and the signal-to-noise ratio is not excessive.
Abstract: Knowledge of the atmospheric transmission precisely at laser emission wavelengths is very important in many laser experiments. Over horizontal propagation paths a direct measurement of the transmission using the laser source can be made. A vertical propagation path through the entire atmosphere presents a more difficult measurement problem at the requisite spectral resolution. At present, the most reliable transmission coefficients are calculated using atmospheric models. It is the purpose of this letter to show that a laser heterodyne radiometer can be used to measure accurately the atmospheric transmission for laser radiation propagating through the entire atmosphere. Measurements, with a spectral resolution of 7 × 1 0 4 c m 1 , are presented for the P(20) C O2 1 6 laser line and compared with the calculated values. In a recent article, McElroy has discussed the use of a laser radiometer receiving solar radiation for measuring the atmospheric transmission and for making solar temperature measurements. He indicates that an adequate signal-to-noise ratio can be achieved by chopping the incident radiation and synchronously detecting the heterodyne signal. In the present work, the emphasis is on the measurement of the atmospheric transmission coefficient close to the center of the CO2 gaseous absorption line. For this purpose the spectral bandwidth must be small and, consequently, the signal-to-noise ratio is not excessive. Our expression for the postdetection signal-to-noise ratio differs slightly from that of McElroy because we chose a different postdetection correlation (sinusoidal modulation and correlation) and included a geometric factor χ. The factor χ, which is unity for an extended source and is less than unity for a finite source, has been calculated by Yura as a function of the detector size and Fig. 1. Block diagram of the laser heterodyne radiometer.
TL;DR: In this paper, the results of measurements of the far-infrared background radiation made with a balloon-borne radiometer at an altitude of 44 km were obtained. But the results confirmed the results from prior flights, in particular, that a substantial amount, and perhaps all, of the radiation above 13 per cm is due to the atmosphere.
Abstract: Results of measurements of the far-infrared background radiation made with a balloon-borne radiometer at an altitude of 44 km. Equivalent blackbody temperatures were obtained for the background radiation in three bandwidths: 1 to 11.5 per cm, 1 to 13.5 per cm, and 1 to 18.5 per cm. The total measured flux in the largest of these bandwidths is dominated by the atmospheric emission by ozone and water. The data obtained confirm the results of prior flights, in particular, that a substantial amount, and perhaps all, of the radiation above 13 per cm is due to the atmosphere.
TL;DR: In this article, a method for developing and constructing a cloud cover indicator system is described, which involves pointing an IR radiometer vertically downward to a movable mirror and measuring the reflected sky radiation by comparing the difference in thermal radiance between clouds and the sky.
Abstract: A method for developing and constructing a cloud cover indicator system is described. The method involves pointing an IR radiometer vertically downward to a movable mirror and measuring the reflected sky radiation by comparing the difference in thermal radiance between clouds and the sky. To determine cloud cover it is only important to have a threshold value for the clear sky. A value for the coverage is produced by a sunning system summation of all signal lengths of one cycle.
01 Nov 1973
TL;DR: In this paper, false-color images of microwave brightness temperatures obtained from a scanning radiometer operating at a wavelength of 1.55 cm demonstrate the capability of scanning radiometers for mapping snowfields.
Abstract: During March of 1971, the NASA Convair 990 Airborne Observatory carrying microwave radiometers in the wavelength range 0.8 to 21 cm was flown over dry snow with different substrata: Lake ice at Bear Lake in Utah; wet soil in the Yampa River Valley near Steamboat Springs, Colorado; and glacier ice, firm and wet snow on the South Cascade Glacier in Washington. The data presented indicate that the transparency of the snow cover is a function of wavelength. False-color images of microwave brightness temperatures obtained from a scanning radiometer operating at a wavelength of 1.55 cm demonstrate the capability of scanning radiometers for mapping snowfields.
TL;DR: In this paper, the authors describe the latest satellite techniques of photographing the weather and geography of the Antarctic, including the VHRR (very high resolution radiometer), which can resolve 3-km features with scanning radiometers instead of television cameras.
Abstract: This brief note describes the latest satellite techniques of photographing the weather and geography of the Antarctic. Weather satellites normally orbit too high up to produce high-resolution pictures. A recent satellite, NOAA-2, can resolve 3-km features with scanning radiometers instead of television cameras. Conventionally, higher resolution could be provided by the ERTS-A satellite, with pictures covering 185 square km at 70M, resolution, although the same area is covered only every 18 days. A compromise is available on NOAA-2, with the VHRR (very high resolution radiometer), which can resolve 1km, in a 2200 km square area, in either visible or infrared channels. An example is given of a picture in both channels of the Ross Ice Shelf area. These show what appears to be stable 150 km, long flows of warm air down glacier valleys. Another set of pictures shows, with a photographic enlargement of a radiometer scan, new detail in an ice shelf, where the existing maps of the area are shown to be incorrect. /TRRL/
TL;DR: In this article, a correction due to sea surface roughness and nadir angle of viewing is required to obtain the temperature gradient normal to the interface, resulting in an error of 8% for 10m/sec wind and 20° nadar angle.
Abstract: Two-wavelength radiometric measurements of heat flux as developed by McAlister require corrections under rough sea conditions. One correction stems from the increase in sea surface area compared with a horizontal plane. Another correction due to sea surface roughness and nadir angle of viewing is required to obtain the temperature gradient normal to the interface. For example, these errors combined amount to 8% for 10-m/sec wind and 20° nadir angle. Vertical advection associated with convergence and divergence due to wave motion and turbulence generally have negligible effect on the two-wavelength radiometric measurement of heat flux but can possibly become significant for capillary waves and strong convection.
TL;DR: In this paper, a 4-channel radiometer and polarization analyser were used to detect solar radio bursts at around 12 m. The time and frequency resolutions were 10 ms and 100 kHz respectively.
Abstract: Solar radio bursts were observed with a 4-channel radiometer and polarization analyser at wavelenghts around 12 m. The time and frequency resolutions were 10 ms and 100 kHz respectively. Observations on the duration, time profile and frequency splitting are described.
TL;DR: In this paper, a far infrared radiometer cooled by superfluid helium was launched on a rocket from the Kauai Test Range Facility, Kauai, Hawaii, on May 17, 1972.
Abstract: ON May 17, 1972, at 0112 HST a far infrared radiometer cooled by superfluid helium was launched on a rocket from the Kauai Test Range Facility, Kauai, Hawaii. Photometric measurements of the night sky background were successfully made in three spectral regions: 6 to 0.8 mm (bolometer 1), 6 to 0.6 mm (bolometer 2) and 6 to 0.3 mm (bolometer 3). Here we describe the results of this experiment, which yielded a background flux consistent with a 2.7 K blackbody source.
TL;DR: This work investigates the performance of an all-digital, total-power radiometer (TPR), consisting of RF, mixer, and IF stages followed by an analog-to-digital converter (ADC) and shows a good approximation is developed which compares favorably with the exact results under certain conditions.
Abstract: This work investigates the performance of an all-digital, total-power radiometer (TPR), consisting of RF, mixer, and IF stages followed by an analog-to-digital converter (ADC). Square-law detection and smoothing is performed in a digital computer. A figure of merit, the degradation factor, is defined which compares the digital TPR with an ideal analog TPR. Exact results are obtained which include the effects of saturation, finite step size, and finite sampling rate of the ADC. A good approximation is developed which compares favorably with the exact results under certain conditions. The use of a general digital filter for smoothing is considered. A new parameter, the ?equivalent summation number?, is shown to be analogous to the equivalent integration time of an analog TPR.
TL;DR: In this paper, the airborne mapping of hailswaths with both fixed beam and scanning IR radiometers is described, and the results show that the haliswath derived previously from fixed beam data was similar to the one derived from extensive manner data.
Abstract: Further results on the airborne mapping of hailswaths with both fixed beam and scanning IR radiometers are described. It was ascertained that the scanning radiometer made a valuable contribution toward the determination of the structure of the hailswath. The results show that the haliswath derived previously from fixed beam data was similar to the one derived from extensive manner data. Two hailswaths mapped in June 1971 were studied extensively. The dimensions, orientation and fine-structure of the hailswaths, as revealed by IR radiometry, are discussed.
TL;DR: The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm as discussed by the authors.
01 Jan 1973
TL;DR: It was concluded that it is possible to design a highly efficient antenna for radiometer use and to measure its parameters precisely, however, it was found that it was necessary to modify the conventional definition of beamwidth somewhat if this term is to be meaningful for radiometers applications.
Abstract: Horn antennas of four types: pyramidal corrugated, conical corrugated, pyramidal dual mode and conical dual mode, have been constructed and evaluated for use as S-band radiometer antennas. Each of the structures is described and radiation patterns and impedance and resistive loss measurements including a layer of foreign material on a thin radome, are presented. A precision method for determining reflection losses is described using a multiprobe reflectometer technique. The same technique is also applied to the measurement of resistive losses by closing the ends of the antennas with short circuit plates and determining the losses from an accurate measurement of the reflection coefficient. The radiation patterns were recorded with the aid of a real-time digital computer. The stored patterns were then processed to yield gain and beam efficiency. It was concluded that it is possible to design a highly efficient antenna for radiometer use and to measure its parameters precisely. However, it was found that it is necessary to modify the conventional definition of beamwidth somewhat if this term is to be meaningful for radiometer applications.
01 Aug 1973
TL;DR: In this article, noise from solid state noise-diode is coupled into receiver through directional coupler and square-wave modulated at low rate using noise-additive technique.
Abstract: Use of input switch and noise reference standard is avoided by using noise-adding technique. Excess noise from solid state noise-diode is coupled into receiver through directional coupler and square-wave modulated at low rate. High sensitivity receivers for radioastronomy applications are utilized with greater confidence in stability of radiometer.
01 Nov 1973
TL;DR: In this article, a composite surface scattering theory is investigated to compute the emmision and scattering characteristics of ocean surfaces and the effects of clouds and rain on the radiometer and scatterometer observations are also investigated using horizontally stratified model atmospheres with rough sea surfaces underneath.
Abstract: In the microwave region combined active (scatterometer) and passive (radiometer) remote sensors over the ocean show promise of providing surface wind speeds and weather information to the oceanographer and meteorologist. This has aroused great interest in the investigation of the scattering of waves from the sea surface. A composite surface scattering theory is investigated. The two-scale scattering theory proposed by Semyonov was specifically extended to compute the emmision and scattering characteristics of ocean surfaces. The effects of clouds and rain on the radiometer and scatterometer observations are also investigated using horizontally stratified model atmospheres with rough sea surfaces underneath. Various cloud and rain models proposed by meteorologist were employed to determine the rise in the microwave temperature when viewing downward through these model atmospheres. For heavy rain-fall rates the effects of scattering on the radiative transfer process are included.
01 Jan 1973
TL;DR: The Apollo 17 infrared scanning radiometer (ISR) experiment for mapping lunar surface thermal emission is reported in this article, where the instrument, the surface coverage, and the data obtained are discussed.
Abstract: The Apollo 17 infrared scanning radiometer (ISR) experiment for mapping lunar surface thermal emission is reported. The instrument, lunar surface coverage, and the data obtained are discussed.