Showing papers on "Radiometer published in 1989"

Industrial microwave sensors

Abstract: Surveys the different types of microwave sensors and reviews the latest developments reported by European institutes and companies. Attention is given to resonator, transmission, reflection, radar, and radiometer sensors, and to active imaging. >

Microwave Radiometer Systems: Design and Analysis

Abstract: Assuming a familiarity with the basics of radiometry, this work concentrates on practical, not theoretical experiences dealing with radiometers for sensing the surface of the earth Topics include: sensitivity and accuracy, block diagram level, the TUD noise-injection, calibration, imaging, spacebor

Global, seasonal cloud variations from satellite radiance measurements. I: Sensitivity of analysis

Abstract: Global, daily, visible and IR radiance measurements from the NOAA-5 Scanning Radiometer (SR) are analyzed for the months of January, April, July and October, 1977 to infer cloud and surface radiative properties. In this paper, the data and analysis method are described. A unique feature of the method is that it utilizes radiative transfer models that simulate the SR measurements using explicit parameters representing the properties of the surface, atmosphere, and clouds. The accuracy of all the results depends primarily on the proper separation of the total radiance distribution into those parts representing clear and cloudy scenes.

Detectability of Spread-Spectrum Signals

Abstract: Methods of detecting spread-sprectrum signals without knowledge of the pseudorandom code used to generate the signal are described. Exact and approximate methods of calculating relationships among detection probability, false alarm rate, and signal-to-noise ratio are given for radiometers and for channelized pulse-detection systems. The detection performance of the radiometer is compared graphically with that of pulse-detection systems, for two different kinds of pulse detection decision rules. Detection performance as a function of certain signal parameters is shown to be very different for a pulse-detection system than for a radiometer, and this difference in behavior provides a basis for selecting signal parameters that minimize the probability of detection. The reasoning that underlies the selection process is explained, and the process is outlined for each of several signal parameters.

Theoretical algorithms for satellite‐derived sea surface temperatures

Abstract: Reliable climate forecasting using numerical models of the ocean-atmosphere system requires accurate data sets of sea surface temperature (SST) and surface wind stress. Global sets of these data will be supplied by the instruments to fly on the ERS 1 satellite in 1990. One of these instruments, the Along-Track Scanning Radiometer (ATSR), has been specifically designed to provide SST in cloud-free areas with an accuracy of 0.3 K. The expected capabilities of the ATSR can be assessed using transmission models of infrared radiative transfer through the atmosphere. The performances of several different models are compared by estimating the infrared brightness temperatures measured by the NOAA 9 AVHRR for three standard atmospheres. Of these, a computationally quick spectral band model is used to derive typical AVHRR and ATSR SST algorithms in the form of linear equations. These algorithms show that a low-noise 3.7-μm channel is required to give the best satellite-derived SST and that the design accuracy of the ATSR is likely to be achievable. The inclusion of extra water vapor information in the analysis did not improve the accuracy of multiwavelength SST algorithms, but some improvement was noted with the multiangle technique. Further modeling is required with atmospheric data that include both aerosol variations and abnormal vertical profiles of water vapor and temperature.

Personal UV radiometer

Abstract: A miniaturized portable battery operated combined power/energy radiometer appropriate for personal use provides a convenient means for determination of the direction of maximum radiant UV power and the measurement of the total energy over time or dosage. The radiometer possesses particular usefulness for sunbathers, walkers, and other persons who are exposed to ambient radiation. Suitably the radiometer includes means for attachment to an article of clothing and/or a positionable stand.

Instrument description of the airborne microwave temperature profiler

Abstract: The microwave temperature profiler (MTP) is a passive microwave radiometer installed in the NASA ER-2 aircraft and used to measure profiles of air temperature versus altitude. It operates at 57.3 and 58.8 GHz, where oxygen molecules emit thermal radiation. Brightness temperature is measured at a selection of viewing elevation angles every 14 s. MTP was the only remote sensing experiment aboard the ER-2 during the Airborne Antarctic Ozone Experiment. This paper describes hardware, calibration, and performance aspects of the MTP.

Optical and microphysical properties of a cold cirrus cloud : Evidence for regions of small ice particles.

Abstract: An airborne lidar and a scanning radiometer aboard an ER-2 aircraft were used to observe a cold cirrus cloud, and a Forward Scattering Spectrometer Probe (FSSP) was used to obtain simultaneous in situ microphysical observations at two altitudes within the cloud. Lidar depolarization ratio data show that the clouds were composed predominantly of ice crystals. At an altitude where the temperature was -62.7 C, the lidar and radiometer analysis gave a visible extinction to infrared absorption ratio (alpha) of 2.3, while the cloud microphysics data provided an alpha value of 3.77. The discrepancy is attributed to undersizing of particles by the FSSP. Direct and remote measurements showed better agreement for a lower layer where the temperature was -47.3 C.

A multifrequency microwave radiometer of the future

Abstract: A description is given of a passive microwave remote sensing system designed to meet the observational needs of Earth scientists in the 1990s. This system, called the high-resolution multifrequency microwave radiometer (HMMR), is to be part of a complement of instruments in polar orbit that will form the Earth Observing System (Eos). As presently envisioned, the HMMR will consist of three separate instruments. These are the advanced microwave sounding unit (AMSU) presently under development for NOAA (US National Oceanic Atmospheric Administration), the advanced mechanically scanned radiometer (AMSR), and the electronically scanned thinned array radiometer (ESTAR). The AMSU will provide atmospheric soundings of temperature and water vapor using channels in the oxygen resonance band (50-60 GHz) and water vapor resonance line at 183 GHz. The AMSR is to be a microwave imager including channels at approximately 6, 10, 18, 21, 37, and 90 GHz, each with dual (linear) polarization. The ESTAR is an imaging radiometer operating near 1.4 GHz designed to obtain global maps of surface soil moisture with spatial resolution on the order of 10 km. >

Radiometric and Geometric Calibration of a Visible Spectral Electro-Optic “Fisheye” Camera Radiance Distribution System

Abstract: Camera systems which measure a complete hemispherical field (“fisheye” lens systems), can be applied to the measurement of the radiance, but accurate radiometric and geometric calibrations are required to obtain absolute radiance data. The calibration procedure applied to an instrument built for spectral and geometrical radiance distribution measurements in the visible wavelength region (450–650 nm), based on an electro-optic fisheye camera system, is described and validated through comparison with a mere standard radiometer.

Titan atmospheric composition by hypervelocity shock-layer analysis

Abstract: The Cassini Mission, a NASA/ESA cooperative project which includes a deployment of probe into the atmosphere of Titan, is described, with particular attention given to the shock radiometer experiment planned for the Titan probe for the analysis of Titan's atmosphere. Results from a shock layer analysis are presented, demonstrating that the mole fractions of the major species (N2, CH4, and, possibly Ar) in the Titan atmosphere can be successfully determined by the Titan-probe radiometer, by measuring the intensity of the CN(violet) radiation emitted in the shock layer during the high velocity portion of the probe entry between 200 and 400 km altitude. It is shown that the sensitivity of the CN(violet) radiation makes it possible to determine the mole fractions of N2, CH4, and Ar to about 0.015, 0.003, and 0.01, respectively, i.e., much better than the present uncertainties in the composition of Titan atmosphere.

Representativeness errors for radiosonde observations

Abstract: SUMMARY Data from the United Kingdom operational upper air network, as well as from special radiosonde trials, have been analysed to provide statistics of spatial and temporal atmospheric variations. These statistics are applied to a study of the network performance and of representativeness errors associated with the use of the data in synoptic analysis. The results also have application to comparisons between measurements from radiosondes and those from other observing systems. For example, it is demonstrated that minimum collocation errors associated with radiosonde temperature measurements located at the centre of a satellite radiometer scan spot of radius 55 km are <1 degC for levels in the troposphere and lower stratosphere.

Optical power calibrator based on a stabilized green He-Ne laser and a cryogenic absolute radiometer

Abstract: An optical power calibrator is described whose overall calibration uncertainty is less than 10/sup -4/ for an optical power of 0.13 mW. The laser light source of the system operates at a wavelength of 543.5 nm, being close to the wavelength at which the candela is defined, 555 nm. A stable optical power is achieved by stabilizing the intensity and the frequency of a green He-Ne laser. The optical power is detected by a cryogenic absolute radiometer based on the principle of electrical substitution radiometry. It can be used to measure up to 0.5 mW in the visible and near-infrared region with a 3 sigma uncertainty of about 5*10/sup -5/. The factors limiting the overall uncertainty of the calibrator are analyzed: the conductance fluctuations of the temperature sensor in the absorption cavity and the beam scatter are found to be the most significant error sources. Limited absorptivity of the cavity (0.99998) and the background radiation cause additional uncertainty. The system is controlled by a microcomputer with self-check and autocalibration features. >

Global, Seasonal Surface Variations from Satellite Radiance Measurements

Abstract: Global, daily, visible, and infrared radiance measurements from the NOAA-5 Scanning Radiometer (SR) are analyzed for the months of January, April, July, and October 1977 to infer surface radiative properties. A radiative transfer model that simulates the spectral and angular characteristics of the NOAA-5 SR measurements is used to retrieve monthly mean surface visible reflectances and temperature at 25 km resolution. These surface properties were found sufficiently accurate for simulation of clear sky radiances to determine global, seasonal variations in cloudiness. Further comparisons of these results with other data highlight the analysis difficulties and radiative model shortcomings that must be overcome to monitor regional and seasonal variations of earth's surface. These preliminary results also provide an estimate of the magnitude of these variations.

Comparison of NOAA/AVHRR-2 sea surface temperatures with surface measurements in coastal waters

Abstract: Sea surface temperatures (SSTs) derived from the Advanced Very High Resolution Radiometer (AVHRR-2) on the NOAA-7 and NOAA-9 satellites arc compared with measurements taken from a boat in coastal waters off Fremantle, Western Australia. The satellite temperatures have been corrected for atmospheric water vapour, using seven published algorithms. The two most appropriate algorithms for our data set result in 'boat-minus-satellite' biases of about 0-2 deg C and —0-1 degC, with R.M.S. errors of about 0-6 deg C. The satellite temperature transects are shown to reproduce satisfactorily the seasonally reversing cross-shelf gradients as well as the finer thermal structure, demonstrating the value of high-resolution satellite SST measurements in continental shelf regions.

Satellite-derived low-level atmospheric water vapour content from synergy of AVHRR with HIRS

Abstract: The infrared sensor systems AVHRR (Advanced Very High Resolution Radiometer) and HIRS (High resolution Infrared Radiation Sounder) on board the NOAA-7 satellite are studied theoretically by means of radiative transfer calculations to enable the development of new retrieval techniques for atmospheric water vapour profiles. Simulations of radiometer signals have been performed for a large set of atmospheres from the middle and tropical latitudes. Subsequent development of a physical-statistical retrieval method demonstrates the usefulness of a coupling of both radiometers for water vapour retrievals in a single HIRS field of view. Total column amounts as well as the amounts in thick layers (150-200 hPa (thick) in the lower troposphere can be derived with an accuracy of 5-15 per cent and 15-25 per cent respectively. The amounts in thinner layers (50hPa) can be estimated with accuracies between 20 and 30 per cent. The AVHRR split window channels are a powerful tool in the water vapour retrievals. The...

Infrared spectroscopy (2-3-20 μm) for the geological interpretation of remotely-sensed multispectral thermal infrared data

Abstract: The spectral radiance and spectral reflectance of natural weathered surfaces of common sedimentary and igneous rocks is determined from in situ and in the laboratory measurements. In situ spectral radiance measurements (5-14 microns) were made with a portable spectral radiometer and were used to derive the spectral emissivity of the rocks. The spectral reflectance measurements (2.3-20 microns) were made in a laboratory with a Fourier transform IR spectrometer with a diffuse reflectance accessory. Good agreement is found between the two techniques. The field portable spectrometer has a larger field of view and the in situ data provide more accurate measurements of the intensity of spectral features related to temperature and atmospheric effects.

Multiwavelength solar radiometer network and features of aerosol spectral optical depth at Trivandrum

Abstract: Five multiwavelength solar radiometers have been developed and deployed at Trivandrum, Mysore, Waltair, Jodhpur and New Delhi establishing a network during Indian Middle Atmosphere Program. The instruments measure atmospheric columnar optical depth at nine wavelengths in the visible and near infrared enabling studies on physical features of aerosols and integrated content of atmospheric water vapor. Using this instrument, measurements of aerosol optical depth and atmospheric water vapor have been made at Trivandrum since November 1985. The monthly, seasonal and spectral variations of aerosol optical depth are studied and their implications are discussed in the light of earlier findings.

Semiempirical model for cloud attenuation prediction

Abstract: This letter presents a semiempirical model for the estimation of annual cumulative statistics of cloud attenuation. The statistics are predicted from ground-based humidity and temperature measurements. Some of the model parameters have been derived from radiometer measurements carried out at 20 and 30GHz.

Novel correlation radiometer: the length-modulated radiometer

Abstract: The operating principle of a new radiometer is described, which consists of length modulation in a static cell. This development retains the advantages of the pressure modulator but allows higher operating pressures.

Superconducting kinetic inductance radiometer

Abstract: A bolometer that is based on a differential thermometer that senses temperature changes through changes in the kinetic inductance of a superconducting thin film is being developed. The temperature transducer is an inductance bridge patterned as an integrated circuit on a 1-cm/sup 2/ Si substrate. Two inductors from opposite arms of the bridge are patterned on a 2-mm/sup 2/ thermally isolated Si island which is supported by a 9- mu m thick Si:B membrane. The bridge is excited with audio-frequency current, and the bridge imbalance is detected with a commercial DC SQUID amplifier. The bridge is balanced by applying power to the thermally isolated island. This thermometer is the sensor for a prototype radiometer that will provide an absolute measure of IR power. The radiometer, which is designed for a NEP of about 10/sup -11/ W/ square root Hz, is intended to measure the spectrally dispersed power of a 300-K black body. This absolute radiometer is being developed for use at the Low Background Infrared (LBIR) Facility at NIST, Gaithersburg, MD. The noise floor of the temperature transducer for the radiometer has been measured to be 0.7 pW for a 100-s integration time. This is approximately 150 times lower noise than that of the commercial absolute radiometer currently used at the LBIR facility.

Infrared fibers for radiometer thermometry in hypothermia and hyperthermia treatment

Abstract: One severe problem with heating in hypothermia and hyperthermia treatment is the accurate measurement and control of temperature in the presence of a strong electromagnetic field. For this purpose, a fiber-optic radiometer system based on a nonmetallic, infrared fiber probe, which can operate either in contact or noncontact mode, has been developed. In preliminary investigations, the radiometer worked well in a strong microwave or radiofrequency field, with an accuracy of +or-0.5 degrees C. This fiber-optic thermometer was used to control the surface temperature of objects within +or-2 degrees C. >

Integrated structural electromagnetic shape control of large space anatenna reflectors

Abstract: The requirements for extremely precise and powerful large space antenna reflectors have motivated the development of a procedure for static shape control of the reflector surface. A mathematical optimization procedure has been developed that improves antenna performance while minimizing necessary shape-correction effort. The control procedure is based on regulating electromagnetic (EM) performance in contrast to previous work, which is based on controlling the rms distortion error of the surface, thereby indirectly improving antenna performance. The application of the control procedure to a radiometer design with a tetrahedral truss backup structure demonstrates the potential for significant improvement. The results indicate the benefit of including EM performance calculations in procedures for shape control of large space antenna reflectors.

Lake area measurement using AVHRR A case study

Abstract: We note the importance of remote sensing of lake level and area changes for climate research; we discuss the initial need to monitor level and area simultaneously, and note that ERS-1 will be suitably equipped for the task, carrying a radar altimeter and the Along-Track Scanning Radiometer (ATSR). A simple area measurement technique is investigated and we show that the area of Lough Neagh (area 390 km2) can be measured using data from the Advanced Very High Resolution Radiometer (AVHRR) instrument (similar to ATSR), by using channel-2 in the day and channels-4 and -5 at night, to an accuracy of ∼ 1 per cent, which is well within our estimates for the requirement.

Comparing SMMR and AVHRR data for drought monitoring

Abstract: Coincident Scanning Microwave Multi-channel Radiometer 37 GHz and Advanced Very High Resolution Radiometer normalized difference vegetation index satellite data have been compared from drought-affected regions of sub-Saharan Africa and northeastern Brazil for the time period of 1980-1985. Although the two satellite data types can be highly correlated, differences between them were found for the Sahel zone in 1985 and for northeastern Brazil from 1984-1985. These findings suggest that scattering or surface roughness contributions may be greater than previously assumed for the 37 GHz microwave data.

Ground-Based Microwave Radiometric Observations of Precipitable Water Vapor: A Comparison with Ground Truth from Two Radiosonde Observing Systems

Abstract: Dual-channel microwave radiometric measurements of precipitable water vapor are compared with values determined from two types of radiosondes. The first type is used in conventional soundings taken by the National Weather Service. The second is used by the CLASS system, as operated by the National Center for Atmospheric Research. The standard deviations of the two comparisons are nearly equal, being about 0.1 cm, but statistically significant biases occur between the radiometer and the radiosondes. A bias of 0.162 cm is present between radiometer and NWS values during the day and 0.075 cm during the night. The comparison shows that significant differences exist between the radiometer and the NWS moisture soundings when the relative humidity drops below 20 percent for pressures greater than 500 hPa. When this situation occurs, the NWS soundings contain a default dewpoint depression value of 30°C. After such data are removed from the comparisons, agreement between radiometer and NWS radiosonde data...

Advanced microwave scanning radiometer (AMSR): requirements and preliminary design study

Abstract: An investigation on users' requirements for future passive microwave scanning radiometers, especially the advanced microwave scanning radiometer (AMSR), which is one of the Earth Observing System instruments, has been conducted together with a preliminary design of the AMSR system. As a result, mission parameters for the AMSR have been determined while the feasibility of the electronically scanning type of AMSR has been confirmed. In particular, it is found that a beam-switching antenna system that was developed makes possible multifrequency measurement, and multiple beam conical scanning, while preserving polarization purity. >

Characterizations Of The Earth Radiation Budget Experiment (ERBE) Scanning Radiometers

Abstract: NASA's Earth Radiation Budget Experiment employs the Earth Radiation Budget Satellite and the NOAA 9 and 10 spacecraft to obtain absolute measurements of incoming solar radiation, shortwave earth-reflected solar radiation, and longwave earth-emitted radiation, using both scanning and nonscanning radiometers. Each of the three remote-sensing spacecraft carry narrow FOV scanning radiometers whose detection sensors are thermistor bolometers. Attention is presently given to the calibration models and methods employed in characterizing the scanning radiometers' output signals; the design features of the scanners and flight calibration systems are presented.

Determination of the spectral radiance of deuterium lamps using the storage ring Bessy as a primary radiometric standard

Abstract: The electron storage ring BESSY is a primary radiometric standard of spectral irradiance, which has been used for the calibration of deuterium lamps as radiometric transfer standards of spectral radiance in the wavelength range 115-350 nm. The radiometer used for these measurements is described in detail. For λ > 165 nm the uncertainty of the spectral radiance of the calibrated lamps is if > 3%.

Comparison of the measured and predicted response of the Earth Radiation Budget Experiment active cavity radiometer during solar observations.

Abstract: The Earth Radiation Budget Experiment consists of an array of radiometric instruments placed in earth orbit by the National Aeronautics and Space Administration to monitor the longwave and visible components of the earth's radiation budget. Presented is a dynamic electrothermal model of the active cavity radiometer used to measure the earth's total radiative exitance. Radiative exchange is modeled using the Monte Carlo method and transient conduction is treated using the finite element method. Also included is the feedback circuit which controls electrical substitution heating of the cavity. The model is shown to accurately predict the dynamic response of the instrument during solar calibration.