Showing papers on "Radiometer published in 1975"

Some Characteristics of the Albedo of Snow

Abstract: Spring snowcovers exhibit a substantial contribution of a specular component to their reflection of solar radiation. This anisotropy can be measured with radiometers with small aperture, here with a TIROS radiometer. Indicatrices thus determined are dependent on solar angle. They are of importance for interpreting albedo values and for reducing air- or spaceborne reflectance data taken under distinct nadir angles.

Seasonal and latitudinal variation of the stratospheric concentration of HNO3

Abstract: A sensitive spectral radiometer system capable of measuring the atmospheric emission in the 6.5µm to 13.0µm region has been constructed for use on the WB57F aircraft used on the Department of Transportation Climatic Impact Assessment Program. The data obtained with this instrument on a number of flights have been analyzed to determine the total HNO3 column density above the aircraft at various latitudes and seasons. Examination of these data indicate a definite variation of HNO3 column density with latitude and possible seasonal variations.

Pioneer 11 infrared radiometer experiment: the global heat balance of jupiter.

Abstract: Data obtained by the infrared radiometers on the Pioneer 10 and Pioneer 11 spacecraft, over a large range of emission angles, have indicated an effective temperature for Jupiter of 125° ± 3°K. The implied ratio of planetary thermal emission to solar energy absorbed is 1.9 ± 0.2, a value not significantly different from the earth-based estimate of 2.5 ± 0.5.

Experimental Determination of Temperature Profiles by Ground-Based Microwave Radiometry

Abstract: A one-week experiment was conducted to evaluate a dual-frequency microwave radiometer for recovering low altitude temperature profiles; the two-channel radiometer operated at 53.5 and 54.5 GHz. Meteorological support included radiosondes, helicopters, and an instrumented 150 m tower. Statistical inversion of 13 radiometer angular scan data sets resulted in an average rms error of 2.0 K up to 3 km for the microwave system. Significant features of thermal inversion structure were recovered. A continuous set of fixed-angle brightness observations correlated well with temperatures measured on the tower. The statistical inversion method and the Backus-Gilbert method were applied to the analysis of the accuracy and the spatial resolution of the ground-based system. Model calculations were performed to estimate the effects of departures from horizontal stratification and of significant time variation in temperature structure during an elevation scan.

An infrared heterodyne radiometer for high-resolution measurements of solar radiation and atmospheric transmission

Abstract: A tunable, Dicke-switched, infrared heterodyne radiometer (IHR) has been designed, fabricated, tested, and used to observe solar radiation and determine the atmospheric transmissivity in the 9- 11-\mu m spectral band. The IHR provides a spectral resolution of 6.7 \times 10^{-3} cm-1, a minimum detectable power level of 2.9 \times 10^{-23} W/Hz, and a temperature resolution of less than 1 K for a source temperature of 1000 K, an IF predetection bandwidth of 100 MHz, and an integration time of 30 s. Detailed design equations and measured IHR performance are presented. The IHR was used to make solar and atmospheric transmission measurements and a vertical path atmospheric attenuation of 2.3 dB has been established under favorable weather conditions. The attenuation of solar radiation due to cloud cover and haze have also been investigated.

Evolution of Gulf Stream Eddies as Seen in Satellite Infrared Imagery

Abstract: Pronounced eddies along the western edge of the Gulf Stream were again observed by the Very High Resolution Radiometer aboard the NOAA-2 satellite. A rare sequence of infrared images obtained over a period of seven days shows for the first time the complete evolution of meanders through the eddy stage.

Antenna pattern corrections to microwave radiometer temperature calculations.

Abstract: 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.

Spectral remote sensing of temperature distribution in semitransparent solids heated by an external radiation source.

Abstract: A spectral remote sensing method for recovering the temperature distribution in semitransparent solids from remotely sensed spectral emission data is studied. An analytical model that relates the emerging spectral intensity from a plane layer of solid heated by an external radiation source to the temperature distribution, spectral radiation properties, radiation characteristics of the interfaces of the solid, and the source is formulated. The temperature profile is expressed in the form of a finite series of Legendre polynomials; and the coefficients are obtained using an optimization scheme that, by iteratively solving the expressions for emerging intensity, reconstructs the distribution that best fits the spectral emission data. The validity and accuracy of the remote sensing method is evaluated by comparing the recovered temperature with independent measurements in two different experiments; one using surface thermocouples only and the other a Mach-Zehnder interferometer. Experimental results are reported for PPG clear float glass and Corning Code 7940 fused silica using a Perkin-Elmer spectrometer and Barnes Spectralmaster radiometer to measure the emerging spectral radiant energy. For clear float glass, the recovered temperatures were a maximum of 1.5% higher than those measured with surface thermocouples. For fused silica, the linear recovered and interferometrically measured temperature profiles agreed well, with the maximum deviation never exceeding approximately 2% up to about 1000 K.

Stratospheric measurements of H2O and the diurnal change of NO and NO2

Abstract: WE have flown a radiometer from a balloon (a detailed description of which will be published elsewhere), which senses infrared emission from minor stratospheric constituents on the atmospheric limb. To provide a vertical profile of their concentration, the input mirror of the radiometer scans between 7° below and 2° above the horizontal, as illustrated in Fig. 1. The vertical field of view is 0.4°. Every 5.5 min the same mirror scans to an internal black body and to a space view at 18° upwards, thereby providing a two-point calibration.

Satellite microwave observations of the Utah Great Salt Lake Desert

Abstract: Microwave data acquired over the Great Salt Lake Desert by sensors aboard Skylab and Nimbus 5 indicate that microwave emission and backscatter were strongly influenced by contributions from subsurface layers of sediment saturated with brine. This phenomenon was observed by Skylab's S-194 radiometer operating at 1.4 GHz, S-193 RADSCAT (Radiometer-Scatterometer) operating at 13.9 GHz and the Nimbus 5 ESMR (Electrically Scanning Microwave Radiometer) operating at 19.35 GHz. The availability of ESMR data over an 18 month period allowed an investigation of temporal variations. Aircraft 1.4 GHz radiometer data acquired two days after one of the Skylab passes confirm the satellites observations. Data from the ESMR revealed similar responses over the Bolivian deserts, which have geologic features similar to those of the Utah desert.

Determination of snow depth and snow extent from NOAA 2 satellite very high resolution radiometer data

Abstract: The NOAA 2 environmental satellite and subsequent environmental satellites provide daily coverage of the earth in the visible (0.6–0.7 μm) and thermal (10.5–12.5 μm) spectral bands. The ground resolution of the very high resolution radiometer is 1 km at nadir. This improved resolution in the visible spectral band permits more detailed observations of snow features than were possible with the previous operational satellites. A visible band image from February 11, 1973, depicts the heavy snow cover in considerable detail in areas from Alabama to North Carolina. Digitized reflectance data from the study area have been compared with prestorm bare ground digitized reflectance data of February 6, 1973, to examine the relation of snow reflectivity to snow depths. A regression analysis of greatest brightness versus greatest snow depth for 201 data pairs produced a power correlation coefficient of 0.86. Reflectance values from snow deeper than 30 cm tended to be uniformly high; values from snow less than 30 cm tended to increase rapidly as snow depth increased.

Thermal radiation from LNG spill fires

Abstract: Seven 6-ft, six 20-ft, and one 80-ft fire tests were conducted. In each case, a circular earth dike having a 1.5-ft rim was constructed and LNG was poured to a level of 6 to 8 in. and ignited. Pertinent recorded experimental data for each 6- and 20-ft test consisted of: (1) flame heights and angles of tilt, from movie films; (2) wind velocity at 5-ft and 50-ft levels; (3) wind direction; (4) LNG level variation with time using float level gauges; (5) wide-angle radiometer readings at various locations; (6) narrow-angle radiometer readings at one or two locations; and (7) temperatures at various locations. For the 80-ft test, the burning and shorting of electrical leads resulted in the loss of data, with the exception of the first three items. Burning rate, flame angle, flame length, radiative properties of LNG flames, variation of radiative flux with distance and fraction of energy radiated are discussed. (LK)

Remote sensing of soil moisture by skylab radiometer and scatterometer sensors.

Abstract: A Skylab experiment was designed to evaluate the feasibility of monitoring the moisture content of the soil from space. Data from various Skylab sensors were collected across two test sites while direct measurements of soil moisture were being made at the surface depths of soil. Correlations were obtained between the moisture content of the soil and radiometer sensors (S193 and S194) and the scatterometer instrument (S193). The high correlations obtained indicate that microwave sensors may be quite useful for such measurements in the future.-

Diffraction losses associated with tungsten lamps in in absolute radiometry.

Abstract: The diffraction losses associated with absolute radiometers were calculated for the case where the source is a tungsten lamp used with a long wavelength suppressing filter. The calculations were done using Blevin’s treatment, which assumes a point source and a single diffracting aperture. We have shown that this treatment is sufficiently accurate for a typical absolute radiometer configuration. The calculations were done for color temperatures in the 1600–3200 K range for three typical glass filters.

A Radiometric Realization of the Photometric Units

Abstract: A description is given of the experimental procedures used to transfer the photometric scales of the National Measurement Laboratory to a radiometric base. Tungsten halogen lamps and gas-filled tungsten-filament lamps, operated at the distribution temperature 2856 K, are calibrated as standards of illuminance by using an electrically calibrated radiometer to measure the irradiance when a filter simulating the V (λ) function is interposed between the lamp and radiometer. A value of 682 lm W-1 has been adopted for Km, the maximum spectral luminous efficiency of radiation, because the measurements have shown that this value gives continuity with the Laboratory's previous scale of luminous intensity. It is expected that the photometric base unit will eventually be redefined so as to provide an exactly known, internationally agreed value for Km.

Self-calibrating radiometer

Abstract: A self-calibrating radiometer comprising a block having a front surface for receiving incident radiation flux, an identically configured rear surface for receiving internally applied heat and a midportion for thermally insulating the rear surface from the front surface, the front surface being capable of absorbing as heat substantially all radiation flux incident thereupon and capable of reradiating substantially all of the absorbed heat, and the rear surface being capable of radiating substantially all heat applied thereto, a thermocouple configuration for sensing the heat radiated by each of the front and rear surfaces, an indicator for indicating any difference in the sensed heat, a heating element for applying enough heat to the rear surface so that no difference in heat radiated by the front and rear surfaces is indicated by the indicator, and a measuring circuit for measuring the heat applied to the rear surface, such measurement being indicative of the radiant flux incident on the front surface

Remote sensing of soil moisture by Skylab radiometer and scatterometer sensors

Abstract: A Skylab experiment was designed to evaluate the feasibility of monitoring the moisture content of the soil from space. Data from various Skylab sensors were collected across two test sites while direct measurements of soil moisture were being made at the surface depths of soil. Correlations were obtained between the moisture content of the soil and radiometer sensors (S193 and S194) and the scatterometer instrument (S193). The high correlations obtained indicate that microwave sensors may be quite useful for such measurements in the future.-

A gain−stabilizing detector for use in radio astronomy

Abstract: Excess noise in total−power radiometers, its origin, and its effect on continuum radio astronomy measurements during data reduction are discussed. The theory of a new type of noise−adding radiometer is presented, and the resulting practical application of the theory in the form of a gain−stabilizing detector is described. It is shown that the performance of this type of noise−adding radiometer can be optimized, quite simply, to yield an effective system temperature which is less than that of an ideal Dicke system.

Use of NOAA environmental satellites to remotely sense ocean phenomena

Abstract: The Very High Resolution Radiometer (VHRR) on board the National Oceanic Atmospheric Administration (NOAA) operational polar orbiting satellites has enabled the National Environmental Satellite Service (NESS) to operationally support oceanographic interest to a greater degree than ever before. The two channel (.6 - .7\mu m and 10.5 - 12.5\mu m) radiometer with a subpoint resolution of 1 km allows for greater detail of measurement of several oceanographic phenomenon. In addition to the polar orbiters NOAA/NESS operates two geostationary satellites each equipped with a Visible Infrared Spin Scan Radiometer (VISSR). This two channel instrument (.55 - .75\mu m and 10.5 - 12.6 \mu m) has opened up the exciting possibility of observing motion of the surface thermal features of the ocean. The future polar satellite system TIROS-N is discussed with reference to its capabilities to provide data and services to the oceanographic community.

Remote Measurement of Aerosol Particle Characteristics and Their Significance to Meteorology

Abstract: Theoretical models for the calculation of the radiative effects of atmospheric aerosols require the inference of such parameters as optical depth, the complex index of refraction and the equivalent size distribution. A polarimeter and a multispectral radiometer are used for local monitoring of aerosols via ground stations, or global monitoring via spacecraft occultation experiments. It is shown that measurements of optical depth at one wavelength as has been the custom, are insufficient to provide useful information for meteorological calculations, and new experiments and instruments must be devised to take advantage of new theoretical developments.

Skylab S-193 Radscat microwave measurements of sea surface winds

Abstract: The S-193 Radscat made extensive measurements of many sea conditions. Measurements were taken in a tropical hurricane (Ava), a tropical storm (Christine), and in portions of extratropical cyclones. Approximately 200 scans of ocean data at 105 kilometer spacings were taken during the first two Skylab missions and another 200 during the final mission when the characteristics of the measurements changed due to damage of the antenna. Backscatter with four transmit/receive polarization combinations and emissions with horizontal and vertical receive polarizations were measured. Other surface parameters investigated for correlation with the measurements included sea temperature, air/sea temperature difference, and gravity-wave spectrum. Methods were developed to correct the microwave measurements for atmospheric effects. The radiometric data were corrected accurately for clear sky and light cloud conditions only. The radiometer measurements were used to recover the surface scattering characteristics for all atmospheric conditions excluding rain. The radiometer measurements also detected the presence of rain which signaled when the scattering measurement should not be used for surface wind estimation. Regression analysis was used to determine empirically the relation between surface parameters and the microwave measurements, after correction for atmospheric effects. Results indicate a relationship approaching square-law at 50 deg between differential scattering coefficient and wind speed with horizontally polarized scattering data showing slightly more sensitivity to wind speed than vertically polarized data.

A new broadband square law detector

Abstract: A broadband constant law detector was developed for precision power measurements, radio metric measurements, and other applications. It has a wide dynamic range and an accurate square law response. Other desirable characteristics, which are all included in a single compact unit, are: (1) high-level dc output with immunity to ground loop problems; (2) fast response times; (3) ability to insert known time constants; and (4) good thermal stability. The detector and its performance are described in detail. The detector can be operated in a programmable system with a ten-fold increase in accuracy. The use and performance of the detector in a noise-adding radiometer system is also discussed.

The radio astronomy experiment on Helios A and B /E 5c/

Abstract: The NASA Goddard Space Flight Center radio astronomy experiment on Helios, identified as Experiment 5c, has sixteen observing frequencies over the range of 26.5 to 3000 kHz. The antenna consists of two extendible 15-m booms, forming an electric dipole, two high-impedance preamplifiers located at the root of the booms, and the 16-channel radiometer. Important information about propagation conditions, such as absorption, scattering and refraction, are expected from observations of radio emission regions at distances between 1 and 0,3 AU.

The significance of the S-193 Skylab experiment using preliminary data evaluation

Abstract: The Skylab S-193 radiometer/scatterometer/altimeter experiment is described. The spaceborne microwave system acquires simultaneous radiometric brightness temperature and radar backscatter data over land and ocean. Application of the data analysis to the planning of the GEOS-C and SEASAT-A programs, observation of hurricane Ava, and evaluation of the sensor inflight performance are discussed in terms of using operationally the spaceborne microwave sensors for sensing earth resources phenomena.

Applications of the Nimbus 5 ESMR to Rainfall Detection Over the Oceans and to Sea-Ice Detection.

Abstract: : The report explores the applicability of the applicability of the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) to rainfall detection over the oceans and to sea ice detection. Two different but complementary approaches are taken - a theoretical approach which involved the theoretical calculations of brightness temperature (t sub b) in a prepared scenario of model atmospheres and surface conditions, and an empirical approach which made use of simultaneous measurements of our parameters of interest from other sensors: WSR-57 radar for precipitation, and images from other satellites (NOAA and LANDSAT) for sea-ice.

Airborne Infrared Radiometry and Hailswaths

Abstract: The method of analysis and display of airborne infrared radiometer data is presented. The method involves recording, enhancing, digitizing, filtering, compressing, calibrating and displaying on contour radiation temperature maps, the ground temperatures measured with a Texas Instrument RS-310 scanning radiometer and a Barnes PRT-6 starring radiometer. The method is applied to the analysis of a hailswath near Fort Morgan, Colo., on 13 June 1972. Final conclusions on the research and operational uses of this technique for the analysis of hailswaths are presented.

Influence of reference source properties on ocean heat flux determination with two‐Wavelength radiometry

Abstract: Multiwavelength infrared radiometers used for determining the heat flux through the ocean surface are generally calibrated by using a near-ambient temperature reference radiation source. Typically these sources have spectral emissivities that are less than unity and wavelength dependent. Analysis of the error produced by using a reference source which only approximates an ideal blackbody indicates that significant errors in the heat flux determination can arise unless the emissive properties of the source are well-known and accounted for.

Studies on the Utilization of Solar Radiation by Crop : I. A photosynthetically active solarimeter devised to use in leaf canopy

Abstract: Most of studies on the utilization of solar radiation by crop stands have been concerned with the total short wave radiation. As visible radiation is selectively absorbed by green leaves, utilizations of photosynthetically active radiation by crop stands would differ from the utilizations of total short wave radiation by them. In order to clear the point, an equipment for measuring photosynthetically active radiation in crop stands was devised. 1. Fifteen photodiodes (SHARP, SBC-102) were used as photo energy detectors. In order to make sensitivities of each element uniform, their load resistances were regulated by trimming potentiometers (JAPAN RESISTOR CO., 1w). The values of load resistances of each elements adopted were between 8 and 10 ohmes. These silicon photodiodes were connected as series to sum out-put of each element (fig. 3). 2. Heat-absoring glass (OHARA KOGAKU CO., HG) was used to cut off infrared radiation. Its spectral characteristic is shown in fig. 1. 3. Having a linear responsibility between light intensity and out-put under the dim light, photodiodes adopted were shaded by the brass net (40 meshes) sprayed black enamel paint to 1% rate of light penetration. 4. The size of the photo-energy detector is 498×29×38 mm3, and its construction is shown in fig. 4. The load resistor was separated from photo energy detector, because the sensitivity must be adjusted by the load resistance in case of changing with time. 5. Calibration of the equipment were carried out with comparison to photosynthetically active radiometer (TOSHIBA, PSZ-1 type) under natural solar radiation. While the equipment had been set in the crop stands and run from July to November 1974, no sensitivity changes were found throughout the periods (fig. 5). 6. The cosine response of the equipment was improved by milky-white acryl plate(fig. 6).