This paper is intended to give the non-specialist a brief overview of the problems addressed and the instrumentation used in space applications of ultraviolet (uv) spectroscopy. Emphasis is placed on those devices which to the author seem to have the most potential for use in the near future.

Passive microwave radiometry shows considerable promise for high resolution sensing of atmospheric parameters of meteorological significance. Microwave radiometry from satellites over ocean areas is particularly successful due to the low emissivity of sea water, which enables accurate measurements of both atmospheric liquid water and water vapor. Over both land and ocean, temperature measurements of atmospheric layers can be made which are quite insensitive to clouds. Although current microwave techniques yield excellent results, future improvements can be expected due to 1) the narrow beamwidth capabilities of microwave antennas, 2) the almost monochromatic character and high sensitivity of microwave receivers, and 3) the wealth of molecular resonances in the microwave spectrum.

Atmospheric constituent vertical profiles have been determined from the height derivatives of their measured emission spectra. Samples of these spectra and derived profiles are shown. Several spectral radiometers have been employed to obtain these data from balloon and aircraft platforms. The radiometers are scanning grating monochromators operated at liquid nitrogen and liquid helium temperatures. The optical properties of these radiometers are discussed. Also the effect of these properties on radiometric accuracy is considered. Finally, a few methods for testing the accuracy of atmospheric data are developed.

This paper describes a recently developed transmissometer that can be used to measure atmospheric extinction in different spectral bands in the visible and infrared spectral regions over field ranges up to 8,000 meters. In addition to functioning as a transmissometer the instrument is capable of measuring remotely the apparent radiance emitted or reflected from objects that are located within the starring field of view. In the normal system configuration the transmissometer/radiometer consists of silicon, InSb, and HgCdTe receivers and two multi-color searchlight sources that together allow transmission or radiance measurements in the spectral region of 0.4 to 14 micrometers. Included in the paper is a description of the equipment, the calibration procedure, a typical field measurement, and a discussion of typical transmission measurement results obtained from a variety of recent field deployments.

The design and effective utilization of many infrared systems now being deployed require a detailed knowledge of the transmission properties of the earth's atmosphere. A measurement system recently used for transmission studies at several infrared laser wavelengths is described. Results of comparisons of experimental data to computer generated atmospheric transmission predictions are presented and discussed. The application of Fourier Transform Spectroscopy (FTS) to atmospheric transmission studies is described and a measurement technique using laser measurements to calibrate high resolution FTS data is presented.

The interface region which lies between the meteorological atmosphere of the Earth and "outer" space is a source of abundant optical radiation. The purpose of this paper is to provide the optical instrumentation engineer with a generalized understanding and a summary reference of naturally-occurring aerospace radiation phenomena. The colors of the radiation extend over the full optical spectrum from ultraviolet through the infrared. The emissions, observed during both day and night times, are rich in Zine and band spectra. The parameterization of atmospheric light by frequency (or photon energy) and by spectral radiance is discussed. The sources of the natural light from the gases of the atmosphere are grouped into four categories: (1) airglow mechanisms, (2) thermal processes, (3) scattering phenomena, and (4) auroral excitations. An overview of the characteristic spectral occurrences and intensities is given.

Many different sophisticated instruments are used throughout the world in ground based, satellite and rocket studies of the visible spectrum of the aurora and airglow. Three different instruments, the all sky camera, spectrophotometer and meridian scanning photometer, serve as examples of the types of devices representing the photographic, spectrophotometer and photometric categories of instruments currently in use. The extensive application of digital techniques, solid state electronics, and minicomputers emphasizes the concept of system development that combines data acquisition and the capability for real time data reduction and analysis.

The status and history of liquid nitrogen and helium cooled optical sensors are reviewed with summary details on those instruments developed and data obtained by this laboratory and our principal contractors. A liquid nitrogen cooled field widened interferometer spec-trometer covering the spectral range 1 - 2.5 μm has been developed to operate on the ground and has the best NESR (yoise Equivalent Spectral Radiance) of all developed sensors: :10-1 t watts/cm2 sr cm-1 for a 10 sec measurement time with 5 cm -1 resolution. Atmospheric emissions limit the advantages of cryogenic technology for ground based observations at longer wavelengths. Aircraft and balloon-borne systems are discussed, but emphasis is placed on the rocket-borne sensors developed and flown under the ICECAP program sponsored by the Defense Nuclear Agency (DNA) and the AFGL. The low resolution (i.e. 4%A) spectro-meters use circular variable filters (CVF) as the spectral resolution element and have the following capabilities: SWIR (1.3 - 5.5 μm), 77° K, 2 scans/sec, NESR ≈10-8 w/cm2 sr pm; LWIR (7 - 25 μm), 4° K, 2 scans/sec, NESR ≈10-11 w/cm2 sr μm @ 20 μm. The high resolution spectrometer is an interferometer cooled with supercritical helium and has the following 1 capability: 4 - 25 μm, Δv = 2 cm-1, 1.3 sec per scan, and the NESR ≈5 x 10-12 watts/cm 2 SR -1

The development of a very versatile, reliable, and sensitive radiometer has provided a tool for performing a variety of significant infrared measurements from ground-based and aircraft platforms in the .8 to 7 μm spectral region. The development techniques of the radiometer, the capabilities of the developed instrument, and some typical target and atmospheric emission measurements are presented in the paper. The instrument design incorporates various techniques to eliminate the need for cooling of the optics and structural parts which avoid the inconveniences and difficulties associated with the operation of cryogenically cooled instruments without significantly sacrificing sensitivity. The radiometer may be used in a selectable spectral wavelength and bandwidth mode, a limited spectral scanning mode, or a tuneable spectral wavelength mode. The various modes of operation are accomplished through the use of interference filters whose spectral characteristics are somewhat adjustable by properly controlling or setting their angular orientation. The simplicity of operation of the instrument has provided a means of measuring atmospheric air-glow emissions and aurorally enhanced emissions in the .8 to 1.75 μm region on a routine basis. Also, through the use of a reticle chopper and background suppression technique, the same radiometer has been adapted for measurements of low energy target emissions in the .8 to 7 μm region.

Spatial rejection is critical when exo-atmospheric or in situ radiometric measurements of faint sources, such as air glow emissions, are made in the presence of relatively intense sources such as the sun, moon, or earth. Scattering from atmospheric molecules and aerosols during evaluation in an earth-bound laboratory makes the high-rejection baffle appear to be less effective than it actually is in the measurement situation. A Monte Carlo computer program "SCAT" was written to predict the effects of atmospheric scattering upon field-of-view calibration measurements of optical baffling systems. It was found that Mie scattering could be reduced in a clean room environment and Rayleigh scattering was determined to be the limiting mechanism in a special chamber designed for off-axis measurements. The background flux at 400 off axis was found to be 1 x 10-9 of the on-axis incident flux for a 5° full-angle baffle when illuminated by a 10.2 cm diameter collimated beam. A two step process was used to measure a baffle response at 40° off axis down to 1 x 10-11 of the on-axis incident flux.

The status of atmospheric remote sensors for monitoring air pollution is reviewed with discussion of active systems such as lidar, differential absorption and Raman, and passive systems such as interferometer spectrometers, gas filter correlation, matched filter correlation and vidicons.

Infrared radiometry and spectroscopy provide information related to many important problems of the upper atmosphere, such as specification of the radiative terms in the energy balance, composition of the atmosphere and transport of chemical species, and the chemical reactions producing the ozone balance. For studies of the stratosphere and higher layers, observations usually must be made above the troposphere; aircraft often are suitable platforms because of their large load carrying capacity, comparatively benign environment, and ability to operate easily at remote locations. Radiometry is useful chiefly in studying radiative energy balance and in measuring constituents, such as water vapor and ozone, which have strong bands with little interference from other molecules. Absorption spectroscopy, with the sun as a source, or emission spectroscopy, using radiation emitted by the atmosphere itself, may be used to detect and measure chemical species with concentrations less than one part per billion. Grating spectrometers and interferometric spectrometers have been used for both emission and absorption spectroscopy. Measurements have been made throughout the infrared. Techniques used for spectroscopy and radiometry from aircraft are discussed and some typical results by various observers are presented to illustrate the range of data which may be obtained.

A system for measuring the spatial, temporal and low resolution (visible and IR) spectral distributions of radiating sources is described. The system has three main subassemblies: A Data Collection system of five standard and special purpose visable and IR scanning cameras; a Preprocessing and Display system capable of handling digital or analog data and containing an interim storage facility; and a Digital Video Processing system. Unique features include data display subsystems which provide grey scale, two configurations of pseudo-color and a 3-D graphical displays. The system can be operated in a real-time or delayed playback mode. Discussed in this paper are the features of the several input devices and the system characteristics and capabilities. The time history of the spatial distribution of source radiance in each of several spectral bands regions can be visually displayed. The display system is used for preliminary analysis and selection of data for off line digital computer analysis.

Two dimensional spatial variations of the night sky in the visible spectrum have been observed at the focal plane of the 48-inch telescope at Cloudcroft, New Mexcio. A calibrated, slow-scan, intensified television type sensor was used with exposure periods of the order of one second. It is believed that these sky brightness variations are not readily observed with film because of temporal smoothing which accompanies the very long exposure periods needed to achieve comparable brightness threshold levels. In this paper, instrumentation and test data are described, and speculations are made on the origin of the sky brightness variations and on the impact on future systems.

This paper discusses a program for remote sensing of air pollutants called "Multispectral Observation of Pollutants System (MOPS)." The broad objective of the program is to photograph "invisible" gaseous pollutants by combining ultraviolet imaging in several spectral bands with portable data processing equipment. Electronic cameras using solid state imaging arrays of large dynamic range will permit very low contrast images to be electronically ratioed and contrast enhanced, thus bringing out pollutant images which are below the contrast threshold of film. Such photographs will allow synoptic coverage of geographic areas providing source, sink, and flow data on pollutants, and will provide reconnaissance and pointing information for other remote sensors. The principle gases to be mapped by MOPS will be ozone (03), sulfur dioxide (SO2) ) and nitrogen dioxide (NO2).