Nonscanning Radiometers Research Articles

Instrument Overview and Radiometric Calibration Methodology of the Non-Scanning Radiometer for the Integrated Earth–Moon Radiation Observation System (IEMROS)

The non-scanning radiometer with short-wavelength (SW: 0.2–5.0 μm) and total-wavelength (TW: 0.2–50.0 μm) channels is the primary payload of the Integrated Earth–Moon Radiation Observation System (IEMROS), which is designed to provide comprehensive Earth radiation measurements and lunar calibrations at the L1 Lagrange point of the Earth–Moon system from a global perspective. This manuscript introduces a radiometer preflight calibration methodology, which involves background removal and is validated using accurate and traceable reference sources. Simulated Earth view tests are performed to evaluate repeatability, linearity, and gain coefficients over the operating range. Both channels demonstrate repeatability uncertainties better than 0.34%, indicating consistent and reliable measuring performance. Comparative polynomial regression analysis confirms significant linear response characteristics with two-channel nonlinearity less than 0.20%. Gain coefficients are efficiently determined using a two-point calibration approach. Uncertainty analysis reveals an absolute radiometric calibration accuracy of 0.97% for the SW channel and 0.92% for the TW channel, underscoring the non-scanning radiometer’s capability to provide dependable global Earth radiation budget data crucial to environmental and climate studies.

Comparison of measurements from satellite radiation budget instruments

Successive radiometers have been flown on spacecraft for measurement of the radiation budget of the Earth and to date have provided data sets which overlap in time over a 25‐year period. Together these data sets cover two cycles of any decadal oscillation and are useful for climate research. However, before multiple data sets can be used, it is necessary first to establish precisions and relative biases of the data sets. Although these instruments were all calibrated with great care, inevitably there are differences between the instruments. Also, instruments change while in orbit due to degradation of optical elements and changes of the detectors. A number of studies have compared measurements between pairs of radiometers in order to establish these differences. In this paper we compile these results and by use of a bar chart demonstrate the traceability of calibration of satellite radiation budget instruments over these two decades. Using this compilation the differences are computed for any two instruments listed. The instruments considered here include the ERBE scanning and nonscanning radiometers, ScaRaB I and II, and the CERES instruments aboard the TRMM, Terra, and Aqua spacecraft. These results are a prerequisite to use of multiple data sets for long‐term studies of climate process. The largest biases are between the ERBS scanning and non‐scanning radiometers, which at the “top of the atmosphere” differ by 5.4 W m−2 for shortwave fluxes and by 5.8 W m−2 for daytime longwave fluxes. The standard deviations of the biases, which define how well the data sets can be connected, are less than 1 W m−2 for longwave and between 1 and 2 W m−2 for shortwave fluxes.

Radiation budget measurements for the eighties and nineties

The Earth Radiation Budget Experiment (ERBE) consisted of a scanning radiometer and non-scanning radiometers on each of three spacecraft. These instruments began flying in October 1984. The nonscanning radiometers continue to operate, providing broadband radiation measurements of the Earth's outgoing longwave radiation and reflected solar radiation, in addition to measurements of the solar output. The Clouds and Earth Radiant Energy System (CERES) features a scanning radiometer, which is an improved version of the ERBE scanning radiometer, and will fly on the Tropical Rainfall Measurement Mission and Earth Observation System platforms in the late nineties. The CERES project will provide not only radiant fluxes at the “top of the atmosphere” (TOA), but also at the surface and will compute radiant flux divergence through the atmosphere.

Intercalibration of two airborne thermal infrared radiometers: TIMS and PRT5. Application to land surface temperature retrieval

Abstract An earlier analysis of the data acquired by TIMS (Thermal Infrared Multispectral Scanner) operating from the NASA C-130 during HAPEX (Hydro-logic Atmospheric Pilot Experiment) MOBILHY experiment, showed that the brightness temperatures for all six channels were too high, and that the magnitude of the error was more or less a function of the aircraft altitude. This problem is certainly due to the ambient air stream which could cool the two blackbodies used as reference targets. To correct the TIMS data, the PRT5 (Precision Thermometer) non-scanning radiometer is used. The PRT5/TIMS comparison is based upon a relationship between a combination of the TIMS surface brightness temperatures, Tt , and the PRT5 surface brightness temperature, T. TIMS and PRT5 corresponding transects are superposed by maximizing the linear correlation between the two sets of temperatures. The correlations are always greater than 0-92. Tc and Tk , the cold and hoi actual blackbody temperatures, can be deduced from the slop...

Dynamic electrothermal model for the Earth Radiation Budget Experiment nonscanning radiometer with applications to solar observations and evaluation of thermal noise

A dynamic electrothermal model of the Earth Radiation Budget Experiment total, nonscanning channels has been formulated and implemented as a computer program. This model, which is a modification of an earlier version, is used to simulate two types of solar observations: those obtained through the solar port during solar calibration and those obtained during the satellite pitchover maneuver in which the sun is observed by the radiometer in its Earth-viewing configuration. New results of both simulations are compared with actual flight data. These results show an improved agreement between the simulated and observed radiometer response over previous simulations. The improvement in these severe cases justifies the modification to the model and establishes its accuracy. Thermal noise has been studied also, using a separate but related model, to evaluate its contribution to the radiative energy absorbed by the active cavity. This study has revealed that scattering of the collimated solar radiation contributes, on average, 0.071 mW during solar calibration and 0.207 mW during the pitchover maneuver. These values represent, respectively, 0.156% and 0.460% of the peak power that enters the cavity (:45 mW). On the other hand, the maximum amounts of diffuse power due to emission from the field-of-view limiter and the aperture plate are, respectively, 0.120 and 0.01 1 mW, which amount to 0.270% and 0.024% of the peak power. Finally, the cavity self-contamination contributes only 0.034 mW, or 0.071%, of the peak power absorbed by the active cavity radiometer. This study confirms the assumption that, due to the geometry of the radiometer assembly and the optical properties of its components, thermal noise is small and well within the range of previous estimates.

The Earth Radiation Budget Experiment: Science and implementation

This paper gives an overview of the Earth Radiation Budget Experiment. The experiment consists of scanning and nonscanning radiometer packages on three spacecraft. One is a satellite with a 57° inclination orbit which processes around the earth once every 2 months. Packages are also flown on the sun‐synchronous NOAA‐F and NOAA‐G operational meteorological satellites. The scanning radiometer includes three channels: shortwave, long‐wave, and total. The nonscanner package encompasses a pair of wide‐field‐of‐view radiometers and a pair of medium‐field‐of‐view radiometers. Each pair consists of a total and a shortwave radiometer. The scientific importance and objectives of the mission are described, including the need for the three spacecraft and the utility of the complementary types of radiometers.

Orbital and cloud cover sampling analyses for multisatellite earth radiation budget experiments

Computer simulations have been performed to determine the geographical and temporal coverage of various satellite orbits and scanning and nonscanning radiometers for earth radiation budget measurements. These results were used to simulate the sampling of a diurnally varying cloud and radiation field for several different satellite systems to estimate errors in regional monthly mean reflected radiation. The combined results indicate that coincient observations with a minimum of one sun-synchronous satellite and a midinclined orbit satellite are needed to obtain the required regional, zonal, and global coverage with sufficient temporal sampling for obtaining accurate estimates of monthly mean reflected solar radiation. Overall, the best sampling capability and lowest errors were obtained with a three-satellite system, i.e., two sun-synchronous satellites with different equatorial crossing times combined with either a 46 or 57-deg orbit satellite. The results from these analyses have been used in defining a joint NASA-NOAA multisatellite mission for an earth radiation budget experiment.

Infrared and reflected solar radiation measurements from the Tiros II meteorological satellite

The Tiros meteorological satellite contains detectors, storage, and telemetry for the measurement of infrared and reflected solar radiation from the earth and its atmosphere. Two separate detector designs are employed: a medium-resolution scanning radiometer and a low-resolution nonscanning radiometer. The spin of the satellite provides the scan line of the medium-resolution radiometer, which is then advanced by the orbital motion of the satellite. Five channels using bolometer detectors and filters to limit the spectral response from 6 to 6.5 microns, 8 to 12 microns, 0.25 to 6 microns, 8 to 30 microns, and 0.55 to 0.75 micron are mounted in a single housing with choppers and pre-amplifers. The spatial resolution is about 40 miles square when viewing the earth directly beneath the satellite. The parameters studied by these spectral regions are, in the same order: radiation emerging in the water vapor absorption band, day and night time cloud cover, albedo, thermal radiation, and visual maps for comparison with television pictures from the vidicon cameras also carried in the satellite. The low-resolution nonscanning radiometer, utilizing a simple unchopped design, measures the blackbody temperature and the albedo of the earth. The field of view of the detector when viewing the earth directly beneath the satellite is a circle of 450-mile diameter and covers part of the area of each picture frame of the wide-field television camera. The detector consists of two thermistors, each mounted in the apex of a reflective Mylar cone which provides optical gain. One thermistor, coated black, responds to both reflected solar radiation and the thermal radiation from the earth; the second reflects solar radiation and responds only to the thermal radiation. The design, calibration, performance, and data reduction of both systems are discussed.