Showing papers on "Radiometer published in 1977"

Thermal and albedo mapping of Mars during the Viking primary mission

Abstract: The behavior of Mars as observed by the Viking infrared thermal mapper (IRTM) is considered. The IRTM is a 28-channel, 4-telescope radiometer that operated in six spectral bands. The studies considered include observations from the interplanetary phase through data collection on November 7, 1976. During this interval, thermal mapping of the whole Martian surface has been possible. Attention is given to polar temperatures, global albedos, predawn temperatures, a thermal inertia contour map, geometry considerations, clouds, aspects of predawn warming, and observations of earth.

Detection of Anisotropy in the Cosmic Blackbody Radiation

Abstract: Anisotropy has been detected in the cosmic blackbody radiation with a 33-GHz (0.9 cm) twin-antenna Dicke radiometer flown to an altitude of 20 km aboard a U-2 aircraft. In data distributed over two-thirds of the Northern Hemisphere, an anisotropy is observed, which is well fitted by a first-order spherical harmonic with an amplitude of (3.5 plus or minus 0.6) x 10 to the -3rd deg K, and direction 11.0 plus or minus 0.6 h right ascension and 6 plus or minus 10 deg declination. This observation is readily interpreted as due to motion of the earth relative to the radiation with a velocity of 390 plus or minus 60 km/sec.

Passive microwave images of the polar regions and research applications

Abstract: Passive microwave images of the polar regions, first produced after the launch of the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR)in December 1972, have become a valuable new source of polar information. Some of the potential applications of this new capability were anticipated. Of these, the sensing of sea ice through clouds and the polar night is probably the most important application for polar research and for operations on the polar seas. Other applications, such as the measurement of certain near-surfaceice sheet parameters, have been formulated more recently. Measurement of various ocean surface parameters is expected from the forthcoming multifrequency microwave observations. Undoubtedly additional uses of passive microwave datawill be conceived and developed. Two remarkable aspects of satellite-borne microwave radiometers are the complete spatial detail obtained by the scanning sensors and the temporal detail provided by continual coverage. For example, the observations of detailed microwave emission patterns over the Antarctic ice sheet should yield information that could not be obtained by surface or even aircraft measurements. Sequences of images produced at three-day intervalsreveal short-term ice sheet and sea ice phenomena that would otherwise be missed.

Nimbus-6 earth radiation budget experiment

Abstract: This paper describes the Nimbus-6 earth radiation budget experiment including its prelaunch calibration and in-flight performance. A preliminary assessment of the data shows the ERB measurement of the solar constant to be 1392 W/m2 which is 1.6% higher than the expected value of 1370 W/m2. Both values are traceable to the cavity radiometer scale. There is a disagreement between the fixed wide-angle and scanning narrow-angle measurements of planetary outgoing longwave radiation flux. Since the scanning channels are calibrated in-flight and show good agreement with previous observations of the Nimbus-3 satellite, the discrepancy is believed to be due to erroneous wide-angle flux estimates. The erroneous estimates may be caused by the misinterpretation of the transfer function for the wide-angle-earth-flux sensing thermopile detectors when viewing the earth which, unlike the prelaunch calibration source, does not fill the field of view of the detector and is not an isotropic radiation source. A field of view factor for the wide-angle channels is determined using an in-flight calibration procedure using the night-time scanning channel longwave radiation flux measurements as the absolute standard. The planetary global albedoes, longwave radiation fluxes, and net radiation are about 30%, 240 W/m2, and −4 W/m2 for the months of July and August 1975, which is in good agreement with previous Nimbus-3 estimates.

A Bispectral Method for Cloud Parameter Determination

Abstract: A technique is presented for determining cloud heights and amounts through the use of simultaneous. infrared and visible satellite radiance data. A set of simultaneous equations are developed which solve for cloud-top temperature (Tcld) and cloud amount (Acld) within the geometric field of view of the sensor. The cloud height is determined by comparing Tcld to upper air soundings, An error analysis is also presented showing the accuracy that can he obtained in Tcld and Acld when uncertainties exist in the measured visible and infrared radiances and in the assumptions required. Actual satellite measurements taken from the NOAA Scanning Radiometer (SR) are input into the technique and run for three specific geographical locations during several seasons where ground-based cloud observations are available. Results show an rms error in cloud amount of 0.2 and in cloud height of 0.5 km for a 75 km×75 km area for all cloud types except cirrus. For this case we have developed alternate solutions which ac...

Apparatus and method for hyperthermia treatment

Abstract: The apparatus and method provides accurate temperature measurement and control of living tissue during hyperthermia treatment The temperature is measured by a radiometer tuned to the frequency bandwidth of an energy source providing energy for heating living tissue The radiometer measures essentially the radiant energy and thereby the temperature of the same volume of living tissue that is heated by the source during the hyperthermia treatment

Estimation of Marine Environmental Parameters Using Microwave Radiometric Remote Sensing Systems.

Abstract: : This is an interim report on an ongoing program to develop a passive microwave system for the remote all-weather measurement of sea surface temperature from a satellite platform. It presents a general method for obtaining optimal linear algorithms for the reduction of multifrequency radiometer data to determine marine environmental variables. The mean square errors in determining the environmental variables are also determined thereby enabling the evaluation of different passive microwave radiometric systems. This method, called the 'Environmental Transfer Function', includes in its analysis the error contributions from three sources: errors in measuring microwave brightness temperature, the statistical variances of the environmental parameters, and uncertainties in the equations used to relate the brightness temperatures to the environmental parameters. The mathematical formulation is first developed and then an example application is given to evaluate the remote sensing capability of selected radiometric systems. (Author)

The Voyager infrared spectroscopy and radiometry investigation

Abstract: The infrared investigation on Voyager uses two interferometers covering the spectral ranges 60–600 cm−1 (17–170 μm) and 1000–7000 cm−1 (1.4–10 μm), and a radiometer covering the range 8000–25 000 cm−1 (0.4–1.2 μm). Two spectral resolutions (approximately 6.5 and 2.0 cm−1) are available for each of the interferometers. In the middle of the thermal channel (far infrared interferometer) the noise level is equivalent to the signal from a target at 50 K; in the middle of the reflected sunlight channel (near infrared interferometer) the noise level is equivalent to the signal from an object of albedo 0.2 at the distance of Uranus. For planets and satellites with substantial atmospheres, the data will be used to investigate cloud and gas composition (including isotopic ratios), haze scale height, atmospheric vertical thermal structure, local and planetary circulation and dynamics, and planetary energy balance. For satellites with tenuous atmospheres, data will be gathered on surface and atmospheric composition, surface temperature and thermal properties, local and global phase functions, and surface structure. For Saturn's rings, the composition and radial structure, particle size and thermal characteristics will be investigated. Comparative studies of the planets and their satellite systems will be carried out.

Global monitoring of stratospheric halogen compounds from a satellite using gas filter spectroscopy in the solar occultation mode.

Abstract: We have analyzed the gas filter radiometer approach for long-term monitoring of stratospheric HCl, HF, CH4, and H2O using solar occultation at selected intervals in the 2–6 μm range. Our analysis shows that this instrument technique is feasible. This conclusion is based on a simulation study in which we evaluated the effect of various experiment errors on retrieval accuracy. The instrument errors used were based on measurements made on a breadboard model gas filter radiometer. The results show that HCl and HF can be measured with an rms error of 10% and CH4 and H2O with an error of 15% over the 10–30-km range.

High-sensitivity infrared heterodyne radiometer using a tunable-diode-laser local oscillator

Abstract: A blackbody heterodyne radiometer using a widely tunable PbSnSe-diode laser as the local oscillator (LO) achieved signal-to-noise performance that was an order of magnitude better than previously reported and only a factor of 2.5 below that obtained with a CO(2)-laser LO. The diode laser system performance was within a factor of 6 of an ideal radiometer. High-resolution blackbody heterodyne absorption spectra of ethylene at 10.6 microm were obtained with a 0.4-sec post-detection integration time by tuning the diode LO in a closed-cycle cryogenic cooler.

A Modified Radiometer for Temperature and Microwave Properties Measurements of Biological Substances

Abstract: The use of radiometers for biomedical applications needs a coherent understanding of thermal signals emitted by the tissues. In this paper, we show first, that some precautions have to be taken when measuring a temperature by the classical radiometric method. For instance, the signal emitted by a lossy material depends on its temperature, permittivity and thickness. This remark allows us to find out a new method for measuring microwave permittivity of liquids when using a Dicke radiometer. We propose a modified radiometric method to determine directly the temperature of the material whatever its reflection coefficient. The applicability of this method is tested with a X band set-up including FET microwave amplifiers. Possibilities of using probes for in situ temperature measurements are discussed.

A Quasi-Optical Receiver Design

Abstract: The design of a completely quasi-optical 1.5 mm aircraft radiometer receiver is discussed in detail. The radiometer beam switching is described as well as a reflection isolator utililizing a reciprocating mirror. A quasi-optical local oscillator injection system using a Folded Fabry-Perot resonator is described and receiver performance levels given.

Atmospheric particulate properties inferred from lidar and solar radiometer observations compared with simultaneous in situ aircraft measurements: a case study.

Abstract: Particulate size and height distributions, complex refractive index and mass loading have been measured and inferred from direct aircraft and indirect lidar-solar radiometer observations made during a unique joint experiment conducted the week of 18 November 1974 in Tucson, Ariz. The aircraft and lidar-solar radiometer measurements were first analyzed independently and the results were then intercompared. Vertical profiles of particulate extinction obtained from the lidar (monostatic) and aircraft measurements were found to be in excellent agreement on both a relative and absolute basis. Lidar (bistatic and monostatic) inferences of particulate mass loading agreed favorably with the aircraft mass monitor measurements. The aircraft and lidar (bistatic) size distribution determinations were found to be similar in shape and agreed in absolute value within an order of magnitude. The mean particle refractive index inferred from the lidar (bistatic) measurements (n = 1.40 − i0.000) agreed with the inde...

Ozone Monitoring with an Infrared Heterodyne Radiometer

Abstract: Measurements of the total burden and of the concentration versus altitude profiles of ozone have been made with a ground-based heterodyne radiometer at Pasadena, California. The measurements were made in the 9.5-micrometer wavelength region, where a strong ozone infrared absorption band exists. The radiometer measured solar absorption at selected wavelengths, with a spectral resolution of 0.001 reciprocal centimeter, equivalent to the half-width of an ozone absorption line at the 10-millibar altitude level. A carbon dioxide laser served as the local oscillator. This technique can be used to gather important data on both tropospheric and stratospheric ozone, which are not readily accessible with other remote-sensing techniques.

Radiometric observations of sea temperature at 2.65 GHz over the Chesapeake Bay

Abstract: The present work describes the various corrections necessary in order to deduce ocean surface temperature from S -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.

Temporal Variations in Atmospheric Water Vapor and Aerosol Optical Depth Determined by Remote Sensing

Abstract: By automatically tracking the sun, a four-channel solar radiometer was used to continuously measure optical depth and atmospheric water vapor. The design of this simple autotracking solar radiometer is presented. A technique for calculating the precipitable water from the ratio of a water band to a nearby nonabsorbing band is discussed. Studies of the temporal variability of precipitable water and atmospheric optical depth at 0.610, 0.8730 and 1.04 microns are presented. There was good correlation between the optical depth measured using the autotracker and visibility determined from National Weather Service Station data. However, much more temporal structure was evident in the autotracker data than in the visibility data. Cirrus clouds caused large changes in optical depth over short time periods. They appear to be the largest deleterious atmospheric effect over agricultural areas that are remote from urban pollution sources.

Microwave brightness spectra of layered media

Abstract: Many natural media are layered at the scale of microwaves. Examples include frozen soil over moist soil, ice over water, and snow over soil. The microwave brightness spectra of such media may exhibit interference patterns. Such patterns have been observed for emission from fresh‐water ice but not for emission from snow or from seasonally frozen soil. Three factors which determine whether interference is detectable are the spectral resolution of the radiometer, the uniformity of layer thickness, and the distinctness of interfaces between layers. Analyses of these factors show that: (1) The radiobrightnesses of layered media vary sufficiently slowly with wave‐length that radiometers designed for the radio‐astronomy bands provide adequate spectral resolution; (2) a variability of layer thickness greater than 15 percent of the free‐space wavelength in the area viewed by the radiometer will effectively eliminate an interference pattern; and (3) a diffuse interface, whose thickness is 15 percent of the free‐spa...

Cloud effects on middle ultraviolet global radiation

Abstract: An Eppley radiometer and a Robertson-Berger sunburn meter are employed along with an all-sky camera setup to study cloud effects on middle ultraviolet global radiation at the ground level. Semiempirical equations to allow for cloud effects presented in previous work are compared with the experimental data. The study suggests a means of defining eigenvectors of cloud patterns and correlating them with the radiation at the ground level.

Very-high-resolution far-infrared measurements of atmospheric emission from aircraft

Abstract: Instrument problems and technical results are discussed for an experiment in which an absolute spectrometric radiometer was flown aboard a NASA aircraft at altitudes of 33,000 to 41,000 ft to measure atmospheric emission in the spectral range from 5 to 40 kaysers with a resolution of about 0.03 kayser apodized. The instrument used was actually a polarizing interferometer, and the atmosphere was observed at fixed zenith angles constant to within plus or minus 0.1 deg. The only problem noted was the spoilage of some interferograms by spikes due to electrical interference from the aircraft radio transmission system. A spectrum of the atmospheric-emission brightness temperature obtained with real-time calibration is examined, and the spectral resolution, S/N ratio, and total instrument efficiency are evaluated. The experimental S/N ratio is estimated to be between 40 and 100.

Dual channel correlation radiometer

Abstract: A radiometer in which independent thermal signals are combined to form first and second receiver channel input signals that are coherent with respect to each other. The first and second receiver channel input signals are independently processed in parallel receiver channels to provide first and second correlation signals, each of which include a thermal signal component and a noise signal component. The first and second correlation signals are then correlated to provide an output signal for the radiometer. If, in the combination of the independent first and second thermal signals to form the first and second receiver channel input signals, the portion of the first thermal signal included in one of the receiver channel input signals is quadrature phase shifted with respect to the portion of the first thermal signal included in the other receiver channel input signal, and, similarly, the portion of the second thermal signal that is included in the other receiver channel input signal is quadrature phase shifted with respect to the portion of the second thermal signal included in the one receiver channel input signal, an improvement in the radiometer sensitivity is realized. Alternatively, if the portion of the first thermal signal included in one receiver channel input signal is phase shifted one hundred eighty degrees with respect to the portion of the first thermal signal included in the other receiver channel input signal, the radiometer will discriminate between the independent thermal signals.

Radiometric observations of sea temperature at 2.65 GHZ over the chesapeake bay

Abstract: The present work describes the various corrections necessary in order to deduce ocean surface temperature from S -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.

Ground truth measurements for thermal infrared remote sensing

Abstract: Since 1971, field measurements have been made in order to establish interpretation keys for remotely sensed thermal infrared radiation in the 9.5 to 11.5 micrometer spectral range. The infrared radiation emitted by different land surfaces has been measured with a Barnes PRT5 radiometer and compared with different environmental parameters (solar radiation, net radiation, air and soil temperature at various depths, air and soil moisture, etc.). The parameters that give the closest correlation with the remotely sensed thermal radiation vary with the type of vegetable cover and with the seasons. The best correlations are obtained with soil surface temperature over bare soil and with air temperature at half the canopy height over vegetated areas. Seasonal variations of regression coefficients between soil surface temperatures and remotely sensed thermal radiation are higher on vegetated areas than on bare soil. /Author/

Radiometric Accuracy in a Forward Looking Infrared System

Abstract: The fundamental question in determining radiometric accuracy in a Forward Looking Infrared (FLIR) system is "What does the detector see?" The answer is that it "sees" with thermal radiation originating from emitting surfaces in a completely enclosed surround by virtue of the various transfer mechanisms -reflection, refraction, and scattering. To achieve high radiometric accuracy, the detector ideally would "see" only the object. However, due to effects such as lens emission, lens surface reflection, mirror surface emission, calibration source reflection (emissivity less than unity), and vignetting, the detector "sees" many other points in the field of view which are interpreted as part of the target itself. Other factors could contribute, e.g., cosn falloff, distortion, and pupil aberrations. From the viewpoint of the detector, all of these are closely related to vignetting, where the detector is partially "seeing" walls and lens mounts together with reduced intensities of radiation from the object scene. The approach here is to determine radiometric accuracy across the field of view on the basis of contributions from geometrically-defined sources outside of the object. Such a spatial spread of detector view must be combined with the temperature distribution to determine the radiometric accuracy of the system as well as image effects such as shading and narcissus. What the detector "sees" is determined by a computerized backward trace of many rays from the detector. To determine the variation across the field of view, this computation is made for a number of rotations of the scan mirrors. In the case of a FLIR designed for imaging and display, a high relative radiometric accuracy is required. For a FLIR used as an absolute radiometer, absolute radiometric accuracy close to the noise equivalent temperature difference of the system is achievable.

Satellite site diversity: Results of a radiometer experiment at 13 and 18 GHz

Abstract: Joint attenuation statistics for a model site-diversity satellite system which would operate at 18 and 30 GHz were gathered in a radiometer experiment conducted at sites near Atlanta, GA, and Denver, CO. The receiver is of the classic Dicke radiometer type, monitoring sky-noise power at 13.6 and 17.8 GHz. Scaling provides the means to derive 30 GHz performance. The experiment, which commenced in May 1973, provides an expedient means of acquiring essential rain attenuation statistics without the use of active signal sources, such as a satellite beacon. This article describes the experiment and presents the results, including representative data samples from the 1½A year measurement period. Based on these measurements, a model satellite system operating during, the measuring period in Atlanta, at 18 and 30 GHz with 8 and 18 dB fade margins, respectively, would require 14-mi site diversity to insure no more than 0.005 percent propagation outage. During the same time period, site diversity was found unnecessary to satisfy this objective with operation in Denver.

The Antarctic Atmosphere as Seen by Satellites

Abstract: A brief review is given of satellite observations of the atmosphere which are relevant to Antarctic studies. Aspects of the behaviour of the Southern Hemisphere during winter are described using Nimbus selective chopper radiometer and pressure modulator radiometer temperature sounding data which extend to mesopause levels. Emphasis is placed upon the new measurements of the mesosphere, and monthly mean Southern Hemisphere maps are given for various heights in the mesosphere during August 1975 and for the months July-September 1975 for the top level near the mesopause. Planetary waves in the Southern Hemisphere are found to propagate to the mesopause with diminution of the temperature amplitude above about the stratopause, and tilt westward with increasing height and decreasing latitude.