Showing papers on "Radiometer published in 1971"

Mariner 1969 infrared radiometer results - Temperatures and thermal properties of the Martian surface

Abstract: The reduced data of the Mariner 6 and 7 Infrared Radiometer Experiments are presented, along with a discussion of the reduction and calibration procedures. Evidence is presented showing that the surface of Mars is strongly nonhomogeneous in its thermal properties, on scales ranging from those of the classical light and dark areas to the limit of resolution of the radiometers. On the sunlit side, the mean thermal inertia, for admissible bolometric albedos, is 0.006 (cal cm^(-2) sec^(-1/2) °K^(-1)). The dark areas Syrtis Major and Mare Tyrrhenum, observed at night, require thermal inertias as high as 0.010. The temperatures measured over the circular basin Hellas require a bolometric albedo of 0.40 and also a high thermal inertia. The temperature measured over the south polar cap, 148° K, provides evidence that the major constituent of the frost deposit is CO_2.

The Response of Terrestrial Surfaces at Microwave Frequencies

Abstract: : The report reviews the basic properties and terrestrial surface responses of microwave sensors, both active (radar) and passive (microwave radiometer). Appropriate surface responses (bistatic coefficient, emissivity etc.) are defined and used to provide general formulas for the system response (receiver power, antenna temperature, doppler spectrum) in terms of system geometry and configuration. The dielectric properties of terrestrial surfaces are reviewed, and data on the complex dielectric constant of rocks, soils and vegetation are tabulated. Theoretical models for surface response are provided for a variety of surface classes, including the surface of uniform layers, the surface with large scale undulation, the slightly rough surface, the surface of individual scatterers (Lommel-Seeliger surface) and the empirical models (Lambert surfaces). Finally, the report includes a large number of typical surface responses at microwave frequencies. Measured bistatic scattering coefficients, radar return, and surface brightness temperature for many terrestrial surface classes are presented and interpreted in terms of the influence of such parameters as surface roughness, dielectric constant, polarization, frequency, angle of incidence etc. on the response.

Remote Sensing of Ocean Currents and Sea Surface Temperature Changes Derived from the Nimbus II Satellite

Abstract: Ocean currents and sea surface temperature remote sensing by Nimbus 2 High Resolution IR Radiometer

Dual frequency radiometer

Abstract: Disclosed is a dual frequency radiometer concept whereby selection of operating frequencies allows the detection and discrimination of metal, water, tarmac, concrete and wet soil from natural terrain backgrounds. Disclosed is one radiometry system designed to detect metal in the presence of background of normal terrain features, including vegetation, ground soil and water. Embodiments of the system are disclosed, employing two radiometer sensing heads operating at different preselected frequencies. The output of each sensing head is mixed with a respective locally generated signal f1 and f2 to produce a common IF frequency and alternately applied to an IF channel. The output of the IF channel is synchronously detected and the difference in level of radiometric energy at the two frequencies is synchronously detected and integrated to produce a difference signal indicative of the presence or absence of metal in the field of view. In one embodiment, the local frequency sources are klystron oscillators and in the second embodiment, solid state Gunn diodes are used. The physical embodiment of one preferred form of sensing head is disclosed. One third embodiment employs a single oscillator and multiplier to produce a second harmonic frequency. The fundamental and the second harmonic are used to serve as reference for the two superhet signal channels. Gain drift, frequency drift and oscillator noise cancellation are all achieved in this embodiment.

The radio astronomy explorer satellite, a low-frequency observatory.

Abstract: The RAE-1 is the first spacecraft designed exclusively for radio astronomical studies. It is a small, but relatively complex, observatory including two 229-meter antennas, several radiometer systems covering a frequency range of 0.2 to 9.2 MHz, and a variety of supporting experiments such as antenna impedance probes and TV cameras to monitor antenna shape. Since its launch in July, 1968, RAE-1 has sent back some 10 billion data bits per year on measurements of long-wavelength radio phenomena in the magnetosphere, the solar corona, and the Galaxy. In this paper we describe the design, calibration, and performance of the RAE-1 experiments in detail.

Stratospheric Warming observed by Nimbus 4

Abstract: Nimbus 4 satellite selective chopper radiometer data on IR radiation emitted by carbon dioxide, considering stratospheric warming

Measurements of the ionization probability of Cu and LaB6 simulated micrometeors

Abstract: Micrometeor mass data from radiometer measurements, detailing Cu and lanthanum hexaboride ionization probability

The detection of ice clouds from remote measurements of their emission in the far infra‐red

Abstract: It is demonstrated that a pair of wavelengths can be chosen in the far infra-red such that the absorbing properties of water-vapour are the same at the two wavelengths while the scattering and absorbing properties of ice particles are different. The results of calculations show that emission from the atmosphere as observed by a satellite radiometer at the two wavelengths will be sensitive to the presence of cirrus cloud. From such measurements of emission near 50μ and 120 μ in wavelength, an indication of the thickness of the cloud can be obtained. Supporting measurements near 2.6 μ will also supply information regarding the particle size in the cloud.

Active cavity radiometric scale, international pyrheliometric scale, and solar constant

Abstract: The active cavity radiometer type II, a new and accurate standard detector, has been developed for the absolute measurement of optical radiant flux. The active cavity radiometric scale (ACRS), defined by the active cavity radiometer (ACR), and the international pyrheliometric scale (IPS), defined by a U.S. standard angstrom pyrheliometer, have been compared in recent experiments. Simultaneous measurements of solar irradiance demonstrated an average systematic difference between the two scales of 2.2%, the measurements on the ACRS exceeding those on the IPS. An analytical study of the sensitivity of the ACR to sources of experimental error is presented. The uncertainty in the ACRS is found to be less than +--0.5% at the one solar constant level relative to the absolute scale based on fundamental physical principles. In August 1968 two ACR's measured the solar irradiance at an altitude of 25 km in a balloon-flight experiment. The solar-constant value derived from this measurement was Ho ---- 137.0 mw/cm . Scales for the measurement of radiant energy are established with respect to fundamental physical concepts by standard detectors or standard emitters of radiant energy. Establishment of a scale of radiomerry by a standard emitter usually involves the irradiance of a suitable (nonstandard) detector by a high-temperature blackbody source of thermal radiation. If the properties of the source and the charac

A Narrow-Beam Radiometer for Atmospheric Radiation Studies

Abstract: The design and performance of a narrow-beam radiometer for atmospheric studies are described. It has a beamwidth of 6 mrad and a minimum detectable radiance of 0.0056 mW cm−2 sr−1 in a 1-HZ output bandwidth. The system incorporates a novel method of comparing flux incident on the aperture against a temperature-stabilized blackbody so that effects due to variations in radiation emitted by or reflected from the chopper blades are eliminated. The radiometer is being applied initially to studies in the 10–12 μm spectral band of the atmospheric “window”. Several applications, including the study of water vapor continuum absorption and the emissivity of high layer clouds, are described briefly.

Laser Radar Reflexions and Downward Infrared Flux Enhancement near Small Cumulus Clouds

Abstract: WE wish to report some interesting simultaneous enhancements of backscattered laser pulses and the downward infrared flux in regions of clear air surrounding small cumulus clouds. The observations were made at Adelaide, South Australia, in March 1970, and at Aspendale, Victoria, in February 1971, but at Aspendale only a radiometer was operated.

Atmospheric pollutant sensing device

Abstract: It has been found that a laser can provide emissions which are absorbed by pollutants, such as NO, NO2, N2O4, SO2 and CO. The laser emission is used to resonantly excite the pollutant molecules and then to act as a local oscillator for a superheterodyne radiometer to detect the fluorescence occurring in response to the stimulation.

Airborne Measurements of Earth Surface Temperature (Ocean and Land) in the 10-12-micro and 8-14-micro Regions.

Abstract: Field experience using infrared radiometers for making airborne measurements of land and ocean surface temperature show that an atmospheric induced error and a surface reflectivity error are present when the 8-14-micro atmospheric window is used. It is generally accepted that the error can be minimized by working in a narrow region of the atmospheric window centered about 10.5 micro. In order to evaluate the improvement in performance using the narrow band filter region, simultaneous airborne measurements were made with two Barnes model PRT-5 infrared radiometers flown side by side over land and water areas for a range of altitudes up to 8000 ft (2440 m). One radiometer contained an 8-14-micro (standard) filter, and the second contained a 10-12-micro filter. Comparison of the data shows the narrow band filter to reduce the measured error 1.5-2.0 times compared with the wide band filter. The data also show that the error increases approximately linearly with altitude, and therefore by taking measurement at two altitudes and linearly extrapolating to ground level, an accuracy of measurement of a few tenths of a degree Celsius is possible.

Radiometric target detection device

Abstract: A radiometer is mounted in a guided missile for detecting electro-magnetichermal power in the microwave region of the spectrum radiated from an area of suspected targets with circuitry coupled thereto to respond to a predetermined change in level of radiation to generate a warhead fuzing signal.

Two-color radiometer

Abstract: The inventive radiometer is capable of measuring the radiant energy of a target or of an event, including a transient event, in two spectral regions with identical fields of view. The invention may be used for target identification or for discriminating against false targets, such as solar radiation.

An Investigation of Cloud Distribution from Satellite Infrared Radiation Data

Abstract: A physical-statistical model using Nimbus II MRIR (medium resolution infrared) radiometer channel 2 (10–11 µm) data is formed to estimate cloud cover. In the model, cloud cover is estimated from the probability density distribution of DV2 values defined to be the differences between the earth surface temperatures and the corresponding channel 2 observed equivalent black-body temperatures. For cloud type estimation, channel 1 (6.4–6.9 µm) and channel 2 (10–11 µm) data are used simultaneously in a joint distribution model. Bivariate DV1 and DV2 frequency distributions portray distinct features associated with different cloud patterns from which it was possible to estimate the cloud coverage for different levels in the troposphere. The major limiting factor in estimating cloud coverage in this study was the areal resolution of the MRIR radiometer. The results indicate that a reliable global climatology may be formed, using higher resolution radiometers combined with irradiance information from other...

Radiometer studies of atmospheric attenuation of solar emission at 19 GHz

Abstract: Frequencies above 10GHz are proposed for earth-satellite communication links, and the planning and operation of such links require a knowledge of the total attenuation produced by the troposphere under various meteorological conditions. A statistical analysis on the attenuation of solar radio emission measured at Slough, Bucks., England, at 19GHz has been carried out for the period June 1968 to May 1970. Data covering this period are presented to show the percentage time for which the attenuation exceeds various values for three cases:(a) measured data covering the range of zenith angles between 28 and 90°(b) the same data normalised to zenith and to a zenith angle of 70° using a cosine normalisation(c) the measured data obtained within 10° ranges of zenith angle.The longest duration of any fade exceeding 10dB was 17 min, recorded in September 1968.

Usefulness of the infrared heterodyne radiometer in remote sensing of atmospheric pollutants.

Abstract: The application of narrow-band optical receivers to the problem of sensing atmospheric pollution is discussed. The emission/absorption lines of many major atmospheric pollutant molecules overlap the operating frequency bands of CO2 laser and CO laser heterodyne receivers. Several remote pollution sensing systems which are based upon utilization of these spectral overlaps are described, and an analysis of their potential is presented. The possibility of using other lasers (e.g.: the PbSnTe tunable diode laser) as local oscillators is also considered. Results of laboratory experiments with a CO2 laser heterodyne radiometer are presented.

Rapid assessment of water pollution by airborne measurement of chlorophyll content.

Abstract: Present techniques of airborne chlorophyll measurement are discussed as an approach to water pollution assessment. The differential radiometer, the chlorophyll correlation radiometer, and an infrared radiometer for water temperature measurements are described as the key components of the equipment. Also covered are flight missions carried out to evaluate the capability of the chlorophyll correlation radiometer in measuring the chlorophyll content in water bodies with widely different levels of nutrients, such as fresh-water lakes of high and low eutrophic levels, marine waters of high and low productivity, and an estuary with a high sediment content. The feasibility and usefulness of these techniques are indicated.

Superfluid-helium-cooled rocket-borne far-infrared radiometer.

Abstract: A far-infrared radiometer, cooled to 1.6 K by superfluid helium, has been flown in a Terrier-Sandhawk rocket. The instrument was designed to measure night-sky radiation in three wavelength passbands between 6 mm and 0.1 mm at altitudes between 120 km and 350 km. A failure in the rocket nose cone separation system prevented the measurement of this radiation, but the performance of the instrument during flight was generally satisfactory. Design features and operational characteristics of the cryogenic, optical, detection, and electronic systems are presented.

A new scanning thermometer

Abstract: A new thermographic apparatus is described. Present infrared techniques have been employed together with a novel optical scanner and a calibrated electronic digital readout system to produce a fast scanning radiometer capable of reading black-body temperatures at the rate of 15000 values per second. The range covered is 27.8-37.4 degrees C in 0.2 deg C steps, or in simultaneous multiple isothermal increments of 1 deg C. The scanning time is 1 s for a field of view 37 cm*30 cm with a spatial resolution of 3 mm. The scanner is fixed focus with a depth of field of about +or-5 cm. The recording error due to mirror variations is less than 0.2 deg C and the noise equivalent temperature less still. A stability of 0.2 deg C has been achieved. The application of this instrument to the assessment of static thermal patterns and dynamic variations is discussed with particular reference to its potential value in medicine.

High Sensitivity Microwave Gated Radiometer for Low Temperature Plasma Afterglow Studies

Abstract: We describe a new microwave gated radiometer for traveling wave measurement of the radiation temperature of low temperature plasma afterglows independent of plasma absorptivity and reflection coefficients. Since this radiometer is unaffected by a medium power heating microwave, it is particularly well suited for keeping a close control on temperature during microwave cross modulation experiments.

Clear air turbulence detectors

Abstract: A radiometer for use in aircraft as part of a clear air turbulence detector apparatus, constructed to provide signals representing the atmospheric temperatures of at least three regions ahead of the aircraft and centered about sight-lines having different angles of elevation or declination with respect to the aircraft, is connected to means for deriving a temperature-difference signal indicating the difference between the measured temperature of a central one of the regions and an average of the measured temperatures of two regions on opposite sides of the central region. The apparatus preferably includes a correction-signal deriving circuit for deriving a correctionsignal dependent upon the local tropopause height at the time of flight and the altitude of the regions subject to temperature measurement and a display for indicating when the temperaturedifference signal differs significantly from the correction signal.

Sea-Surface Temperature Measurements by Infrared Radiometer,

Abstract: After a brief description of Barnes PRT-5 radiometer and of its possible use for seasurface temperature measurments, the results obtained during an oceanographic survey in April 1969 in the Tyrrhenian Sea are presented. The data of the radiometer are compared with those obtained from bucket measurements, applying a statistical method. Satisfactory agreement between the two series of values is found. The influence of the inclination angle of a radiometer on the sea surface temperature measurements is also examined. The results agree with the data previously obtained by other authors.

Calculation of clear-column radiances using airborne infrared temperature profile radiometer measurements over partly cloudy areas

Abstract: In June 1970, a brassboard version of the Infrared Temperature Profile Radiometer (ITPR) was flown on the NASA Convair-990. This flight was made primarily to obtain measurements to test the hypothesis that radiance propagating from clear portions of a partly cloudy field could be calculated directly from the total radiance measurement over the field. Such clear-column radiances are needed if one is to determine the temperature and water vapor profiles of the atmo­ sphere to the earth's surface. Sample results presented herein show these calculations are feasible, and indicate that measurements from the medium resolution scanning radiometers to be used on future polarorbiting satellites can be used to provide global soundings. INTRODUCTION Future Nimbus and ITOS weather satellites are programmed to carry an Infrared Temperature Profile Radiometer (ITPR) for making indirect measurements of the vertical profiles of temperature and water vapor in the earth's atmosphere. The radiation from clear columns of air is required for the derivation of temperature and moisture profiles down to the earth's surface. However, at any given time, most of the earth has broken cloud cover. Since clear columns are few, a method is needed for estimating the equivalent clear-column radiance for the many cases where the radiometers' field of view is partially covered by clouds. Smith (1968) developed a method for calculating the clearcolumn radiance from the observed total radiance. The brassboard version of the ITPR was flown on the NASA Convair-990 during June 1970 to collect data for the purpose of testing this procedure. The brassboard ITPR measures radiance in five narrow spectral channels centered at: (l) 18.8/im, (2) ll.ljUm, (3) 13.k/im, (U) 13.7 |im, and (3>) lU.l/lm. The radiance measured in channel (l), a semi­ transparent region of the rotational water vapor band, is a strong function of the water vapor content of the troposphere. The radiance

Statistical gain fluctuations of microwave amplifiers measured with a Dicke-Radiometer

Abstract: The dependence of the minimum detectable temperatur-difference\(\overline {\Delta T} _{min} \) of a Dicke-radiometer on gain variations in the absence of an input temperature difference is used to measure the spectrum of the low frequency gain variations of variousX-band amplifiers, namely travellingwave tubes (TWT), tunnel-diode amplifiers (TDA) and a mixer IF-amplifier. For a radiometer input temperature difference unequal zero the integral gain variations ΔG/G for TDA's were investigated, and it will be shown that an expression due to Yaroshenko for gain variations of audio amplifiers can be adapted for microwave amplifiers.