Showing papers on "Radiometer published in 1981"

Microwave Remote Sensing - Active and Passive - Volume I - Microwave Remote Sensing Fundamentals and Radiometry

Abstract: The three components of microwave remote sensing (sensor-scene interaction, sensor design, and measurement techniques), and the applications to geoscience are examined. The history of active and passive microwave sensing is reviewed, along with fundamental principles of electromagnetic wave propagation, antennas, and microwave interaction with atmospheric constituents. Radiometric concepts are reviewed, particularly for measurement problems for atmospheric and terrestrial sources of natural radiation. Particular attention is given to the emission by atmospheric gases, clouds, and rain as described by the radiative transfer function. Finally, the operation and performance characteristics of radiometer receivers are discussed, particularly for measurement precision, calibration techniques, and imaging considerations.

Scanning Spaceborne Synthetic Aperture Radar with Integrated Radiometer

Abstract: Spaceborne synthetic aperture radar systems are severely constrained to a narrow swath by ambiguity limitations. Here a vertically scanned-beam synthetic aperture system (SCANSAR) is proposed as a solution to this problem. The potential length of synthetic aperture must be shared between beam positions, so the along-track resolution is poorer; a direct tradeoff exists between resolution and swath width. The length of the real aperture is independently traded against the number of scanning positions. Design curves and equations are presented for spaceborne SCANSARs for altitudes between 400 and 1400 km and inner angles of incidence between 20° and 40°. When the real antenna is approximately square, it may also be used for a microwave radiometer. The combined radiometer and synthetic-aperture (RADISAR) should be useful for those applications where the poorer resolution of the radiometer is useful for some purposes, but the finer resolution of the radar is needed for others.

Albedo, internal heat, and energy balance of Jupiter: Preliminary results of the Voyager Infrared Investigation

Abstract: The in flight calibration of the radiometer and the Michelson interferometer of the Voyager 1 infrared instrument is discussed. The calibrated full disk measurements are applied to derive values of the albedo, the thermal emission and the global energy balance of Jupiter.

Sensitivity of the Total Power Radiometer with Periodic Absolute Calibration

Abstract: The total power radiometer is an attractive choice for imaging applications due to its high sensitivity and simple configuration. However, available theoretical results are inadequate to allow an accurate radiometer performance prediction in the presence of receiver gain fluctuations and other receiver characteristics with nonuniform fluctuation power spectra. An improved analysis of the total power radiometer Delta T is presented in terms of the receiver output fluctuation power spectral density and a transfer function due to postdetection filtering and periodic calibration. Verification of this analysis is obtained by measuring the fluctuation power spectrum of a 94-GHz receiver and comparing the predicted Delta T with a direct measurement. Numerical results including application to an example radiometer system are presented. These results indicate that the total power radiometer should function well in short integration time, periodically calibrated radiometer systems.

Remote Sounding of High Clouds. IV: Observed Temperature Variations in Cirrus Optical Properties

Abstract: The results of a ruby lidar (0.694 μm wavelength) and infrared radiometer (10–12 μm) study on cirrus clouds are reported for a period covering the autumn and winter months at Aspendale (38°S, 144°E). The lidar and radiometer data have been used to study the temperature dependence of the gross structure and optical properties of cirrus clouds. Well-defined correlations are found between the mid-cloud temperature and cloud depth, infrared absorption coefficient, infrared emittance, backscatter to extinction ratio and ratio of the visible extinction coefficient at 0.693 μm to the infrared absorption coefficient at 10–12 μm. For instance, as the mid-cloud temperature varies from −70 to −30°C, the mean cloud depth increases from 1 to 3.5 km and mean infrared absorption coefficient from 0.04 to 0,25 km−1. These two factors together cause a change in emittance from 0.11 to 0.42. The increase in absorption coefficient with temperature can be attributed to the presence of larger ice particles in the deepe...

A three-band hand-held radiometer for field use.

Abstract: A self-contained, hand-held radiometer designed for field use has been constructed and tested. The 4.5-kilogram device, consisting of a strap-supported electronics module and a hand-held probe containing three sensors, is powered by flashlight and transistor radio batteries, uses two silicon and one lead sulfide detector, has three liquid-crystal displays, features sample-and-hold radiometric sampling, and is spectrally configured to Landsat-D9s thematic mapper bands TM3 (0.63 to 0.69 micrometer), TM4 (0.76 to 0.90 micrometer), and TM5 (1.55 to 1.75 micrometers). The device was designed to collect ground-truth data for the thematic mapper and to facilitate ground-based, remote-sensing studies of natural materials in situ. Prototype instruments were extensively tested under laboratory and field conditions, with satisfactory results.

Measurement of reflectance factors under daily and intermittent irradiance variations.

Abstract: A technique for measuring reflectance factors in diurnal and intermittent cloud insolation conditions using hand-held radiometers has been developed. Simultaneously collected reference panel and total insolation measurements were obtained during the South Texas summer growing season (April and May 1980) at Weslaco, Tex., using the GSFC MARK2 three-band hand-held radiometer. The estimated reflectance factors of four reference panels using the hand-held radiometer agreed closely with the expected reflectance as measured with a laboratory spectrophotometer over a wide range of insolation readings (from 20 to 91 mW/cm 2). These results indicate that this technique could prove useful for achieving uniform reflectance factor measurements for remote sensing studies.

CAT Altitude avoidance system

Abstract: A method and apparatus are provided for indicating the altitude of the tropopause or of an inversion layer wherein clear air turbulence (CAT) may occur, and the likely severity of any such CAT, which includes directing a passive microwave radiometer on the aircraft at different angles with respect to the horizon. The microwave radiation measured at a frequency of about 55 GHz represents the temperature of the air at an "average" range of about 3 kilometers, so that the sine of the angle of the radiometer times 3 kilometers equals the approximate altitude of the air whose temperature is measured. A plot of altitude (with respect to the aircraft) versus temperature of the air at that altitude, can indicate when an inversion layer is present and can indicate the altitude of the tropopause or of such an inversion layer. The plot can also indicate the severity of any CAT in an inversion layer. If CAT has been detected in the general area, then the aircraft can be flown at an altitude to avoid the tropopause or inversion layer. The detection method can also be utilized to enable an aircraft to fly at an altitude at which the winds are most favorable for reducing fuel consumption.

Freshwater Ice Thickness Observations Using Passive Microwave Sensors

Abstract: Walden Reservoir, a freshwater lake in north-central Colorado, was overflown six times by a NASA C-130 aircraft between January 1977 and April 1980. The aircraft was equipped with four microwave radiometers operating between 0.81 and 6.0 cm in wavelength (37.0 to 5.0 GHz). The 6.0-cm radiometer data showed a good relationship (R2 = 0.98) with ice thickness based on a sample of four ice thickness values. The 1.67- and 1.35-cm radiometer data showed weaker relationships with ice thickness. The 0.81-cm sensor data showed no positive relationship with ice thickness. None of the relationships was statistically significant because of the small sample size. The 6.0-cm sensor data in the nadir-viewing mode was found to have the most potential of all the wavelengths studied, for use in remotely determining ice thickness. The 6.0-cm radiometer probably sensed the entire thickness of the ice on the reservoir (ranging from 25.4 to 67.3 cm in thickness) and was apparently not significantly affected by the snow overlying the ice. The shorter wavelengths are scattered by the snow overlying the ice and are more suitable for snow studies than for ice thickness studies.

Multichannel scanning radiometer for remote sensing cloud physical parameters

Abstract: An instrument for remote observation of cloud physical properties was designed and fabricated. As part of a larger payload, it was tested in a series of aircraft flights on the NASA CV‐990 in the summer of 1976 and the NASA WB‐57F in the summer of 1979. The instrument is a scanning radiometer with six channels in the near infrared and one channel in the thermal infrared. The optical techniques employed, and the mechanical and electrical design implementation of the instrument, are described. Early results of the data gathered using this instrument are presented to indicate the instrument performance.

Apparatus and method for measuring lung water content

Abstract: A microwave radiometer for the passive, noninvasive measurement of fluid content in animal bodies. The radiometer system includes a ridged waveguide antenna which is responsive to frequencies in the microwave range emitted from the patient's body and is of compact size and light in weight so as to be easily secured to the patient with minimum discomfort and loss of mobility. A heating system is attached to the antenna so as to maintain antenna temperature at approximately the temperature of the patient's body surface. The associated control circuitry processes signals received from the antenna at one or more frequencies and produces an output signal which correlates to the amount of fluid within the measured region of the body.

Estimation of the propagation delay through the troposphere from microwave radiometer data

Abstract: Microwave propagation delay through the troposphere is studied as a means of estimating the adverse effect of atmospheric water vapor on the accuracy of measurements made with very long baseline interferometry. Vertical profiles of temperature and water vapor density were obtained from a total of 240 radiosonde launches taken simultaneously at three New England locations in 1974; all studies were made at the 19 and 22.2 GHz frequency operating range of the radiometers. The wet path length in the zenith direction could be estimated from the surface water vapor density to an accuracy of 5 cm for the summer data and 2 cm for winter data, and with the brightness temperatures, it could be estimated to an accuracy of 0.3 cm. Two dual-frequency radiometers were also used to determine the accuracy of prediction of the path length from real radiometry data. The rms error for the estimation of wet path length from surface meteorological parameters was 3.2 cm, and for the radiometer brightness temperatures the rms error was 1.5 cm.

Method and apparatus for monitoring the burning efficiency of a furnace

Abstract: A furnace burner flame monitoring method and apparatus are provided for controlling the burner fuel mixture in order to operate a furnace at maximum burning efficiency. A radiometer having an infrared detector views the flame and detects infrared radiation emitted from the flame. A filter wheel is interposed between the infrared detector and the flame for transmitting at least three different, discrete, infrared radiation bands from the flame to the detector with the detector thereby generating at least three signals in response to radiation received from the three infrared radiation bands. A control parameter is derived using a ratio of at least two of the signals from the infrared radiation bands which are compensated for flame length using a third of the signals generated by the infrared detector. The control parameter may then be utilized for controlling the fuel/air mixture which is burned for thus monitoring and maintaining the furnace at maximum efficiency.

New correlation radiometer for microwave thermography

Abstract: We describe a new radiometric method capable of reaching a better control of the volume of the tissue under investigation in microwave thermography (this technique is mainly used in biomedical applications). Our process is based on the fact that two (or several) probes with a volume under investigation in common are collecting thermal noise signals which are correlated.

Method of and an apparatus for measuring surface temperature and emmissivity of a heated material

Abstract: When a steel sheet or the like is heated in a furnace to a temperature somewhat higher than the room temperature and is still or moved, its temperature can be measured by detecting the radiant energy therefrom. The measurement is normally difficult due to the influence of background noise of radiant energy from the surroundings, change of the transmittance factor of the environment or atmosphere for radiant energy, and change of the emissivity of the object to be measured. In order to remove such causes of errors and to correctly measure the temperature by detecting radiant energy, a radiometer and a black body radiator are disposed symmetrically and specularly with respect to the normal to a surface of an object to be measured, and two different amounts of radiant energies are emitted from the black body radiator, and the emissivity of the object to be measured is determined from the detected values from the radiometer, the two temperature values of the black body radiator, and the diffusely reflecting factor associated with the object to be measured, whereby correct measurement of the surface temperature of the object to be measured can be done. Embodiments for implementing this method are proposed.

Visible infrared spin-scan radiometer atmospheric sounder radiometric calibration: an inflight evaluation from intercomparisons with HIRS and radiosonde measurements

Abstract: The ability to conduct soundings from a geostationary platform has been demonstrated with the Visible IR spin-scan radiometer Atmospheric Sounder (VAS) aboard GOES-4. While a negative offset reaching 2.0-3.0 C for the upper atmospheric CO2 bands of VAS was observed in comparisons with High Resolution IR Radiation Sounder (HIRS) measurements and analyses of radiosonde data, VAS radiances are consistent with that material. After removing the offset, the temperature profiles derived from VAS radiances agree very well with those observed by radiosondes. Time variations in the atmospheric state are discernible from VAS soundings at three-hour intervals, and were confirmed by radiosonde observations.

Regression Techniques for Oceanographic Parameter Retrieval Using Space-Borne Microwave Radiometry

Abstract: Variations of conventional multiple regression techniques are applied to the problem of remote sensing of oceanographic parameters from space. The techniques are specifically adapted to the scanning multichannel microwave radiometer (SMMR) launched on the Seasat and Nimbus 7 satellites to determine ocean surface temperature, wind speed, and atmospheric water content. The retrievals are studied primarily from a theoretical viewpoint, to illustrate the retrieval error structure, the relative importances of different radiometer channels, and the tradeoffs between spatial resolution and retrieval accuracy. Comparisons between regressions using simulated and actual SMMR data are discussed; they show similar behavior.

Regression Techniques forOceanographic Parameter Retrieval UsingSpace-Borne Microwave Radiometry

Abstract: Variations ofconventional multiple regression techniques areapplied totheproblem ofremotesensing ofoceanographic parame- ters fromspace. Thetechniques arespecifically adapted tothescanning multichannel microwave radiometer (SMMR)launched ontheSeasat andNimbus7satellites todetermine oceansurface temperature, wind speed, andatmospheric watercontent. Theretrievals arestudied pri- marily fromatheoretical viewpoint, toillustrate theretrieval error structure, therelative importances ofdifferent radiometer channels, andthetradeoffs between spatial resolution andretrieval accuracy. Comparisons between regressions using simulated andactual SMMR data arediscussed; theyshowsimilar behavior.

Absolute spectroradiometric and photometric scales based on an electrically calibrated pyroelectric radiometer.

Abstract: An absolute spectroradiometric scale has been developed based on an electrically calibrated absolute detector and silicon detector–interference filter combination. Using the recently adopted definition of the photometric base unit, the candela, the absolute spectroradiometric scale was used to realize a photometric scale, i.e., to calibrate incandescent lamps as luminous intensity standards. These new scales were compared with existing standards and were found to agree to better than 1%.

Large-Angular-Scale Anisotropy in the Cosmic Background Radiation

Abstract: Results of an extended series of airborne measurements of large-angular-scale anisotropy in the 3-K cosmic background radiation are reported. A dual-antenna microwave radiometer operating at 33 GHz flown aboard a U-2 aircraft to 20-km altitude on 11 flights between December 1976 and May 1978 measured differential intensity between pairs of directions distributed over most of the Northern Hemisphere. Measurements show clear evidence of anisotropy that is readily interpreted as due to the solar motion relative to the sources of the radiation. The anisotropy is well fitted by a first order spherical harmonic of amplitude 3.6 + or - 0.5 mK, corresponding to a velocity of 360 + or - 50 km/s toward the direction 11.2 + or - 0.5 hours of right ascension and 19 deg + or - 8 deg declination.

Balloon-borne laser heterodyne radiometer for measurements of stratospheric trace species.

Abstract: Remote measurements of a key stratospheric radical species, chlorine monoxide, have been made with a recently developed balloon-borne instrument: a laser heterodyne radiometer. The characteristics of this instrument, which facilitate its use for measurement of selected trace species in the stratosphere, are described here. The technique of solar occultation in the IR is used to provide the measurement data. This technique is briefly described to point out the high sensitivity and specificity which can be achieved when using a high spectral resolution instrument such as an IR heterodyne radiometer in this manner.

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. I - Theory

Abstract: The theory of deconvolution of wide field-of-view (WFOV) radiometer measurements of earth-emitted radiation provides a technique by which the resolution of such measurements can be enhanced to provide radiant exitance at the top of the atmosphere with a finer resolution than the field of view. An analytical solution for the earth-emitted radiant exitance in terms of WFOV radiometer measurements is derived for the nonaxisymmetric (or regional) case, in which the measurements and radiant exitance are considered to be functions of both latitude and longitude. This solution makes it possible to deconvolve a set of WFOV radiometer measurements of earth-emitted radiation and obtain information with a finer resolution than the instantaneous field of view of the instrument. It is shown that there are tradeoffs involved in the selection between WFOV and scanning radiometers.

Hair dryer with remote sensing temperature control

Abstract: An electric hair dryer having a radiometer which remotely senses the infrared radiation emanating from the hair being dried and which contains a control means that causes the heating means in the dryer to turn off when the infrared radiation indicates the temperature of the hair is about 50° C.

Multichannel Radiometric Determination of Sea Surface Temperature: Parameterization of the Atmospheric Correction.

Abstract: Synthetic computations of atmospheric transmissions and radiant energies are presented in order to simulate remote soundings of the sea surface temperature in two pairs of channels: ∼8.7 and 11.6 μm, on the one hand, and 11 and 12 μm, on the other. This study takes into account absorptions by the line spectra of the various absorbers and by the water vapor continuum, first separately and then simultaneously. In the latter case, the accuracy of the linear parametric retrieval scheme previously presented by Imbault et al. (1978) is shown to depend mostly on the choice of wavelengths for the two channels and two criteria for optimization are introduced. Applying this parametric scheme to the analysis of the experimental results obtained, with the help of an airborne scanning radiometer, over a relatively humid atmosphere within the midlatitudes has led us to conclude that the usual expression for the water vapor absorption coefficient seems to overestimate this phenomenon.

The Solar Maximum Mission

Abstract: The Solar Maximum Mission spacecraft, launched on 1980 February 14, carries seven instruments for the study of solar flares and other aspects of solar activity. These instruments observe in spectral ranges from gamma-rays through the visible, using imaging, spectroscopy, and high-time-resolution light curves to study flare phenomena. In addition, one instrument incorporates an active cavity radiometer for accurate measurement of the total solar radiant output. This paper reviews some of the most important current observational and theoretical questions of solar flare physics and indicates the ways in which the experiments on SMM will be able to attack these questions. The SMM observing program is described.

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. II - Analysis of first year of Nimbus 6 ERB data

Abstract: The theory of deconvolution considered by Smith and Green (1981) is applied to Nimbus 6 data in order to interpret the data with the maximum obtainable resolution. Attention is given to the data sample, sun-contaminated measurements, the measurement model, the deconvolution, the degree variance, the spherical harmonic coefficients, the geographical distribution of longwave radiation, time histories of zonal coefficients, and the effect of a grid system. Degree variance plots for 12 months of longwave radiation data show that the limit for a spherical harmonic representation of the Nimbus 6 wide field-of-view longwave data is 12th degree. The degree variance plots also reveal that most of the power is in the lower degree terms. Contour maps of the radiation field show the geographical distribution of earth emitted radiant exitance for each month.