Image reconstruction from multiple 1-D scans using filtered localized projection.

The state-of-the-art procedure for image acquisition in downlooking remote sensing and astronomical applications is to use scanning linear arrays. These consist of discrete IR solid-state detectors. We consider the spatial resolution that may be attained with such an array. The individual detectors in the array are typically significantly larger than the blur spot of the imaging optics. Hence a naive recombination of data would produce images which are limited in resolution by the size of the detectors. However, the information content of all available data, including intentional overlap of successive scans and rescans of the same area from different directions, may include much higher spatial frequencies. In the following, we outline a method of filtered localized projection (FLP) which attempts to reconstruct these higher frequencies. Mathematically, FLP consists of a localized summation or projection followed by an inverse-filter operation in analogy to filtered backprojection of computed tomography. The FLP method is applied, using a linear array, to simulated data for staggered parallel scans and to multiple scan directions. Effects of noise and limitations of the approach are discussed.

Early results from the infrared astronomical satellite.

For 10 months the Infrared Astronomical Satellite (IRAS) provided astronomers with what might be termed their first view of the infrared sky on a clear, dark night. Without IRAS, atmospheric absorption and the thermal emission from both the atmosphere and Earthbound telescopes make the task of the infrared astronomer comparable to what an optical astronomer would face if required to work only on cloudy afternoons. IRAS observations are serving astronomers in the same manner as the photographic plates of the Palomar Observatory Sky Survey; just as the optical survey has been used by all astronomers for over three decades, as a source of quantitative information about the sky and as a "roadmap" for future observations, the results of IRAS will be studied for years to come. IRAS has demonstrated the power of infrared astronomy from space. Already, from a brief look at a miniscule fraction of the data available, we have learned much about the solar system, about nearby stars, about the Galaxy as a whole and about distant extragalactic systems. Comets are much dustier than previously thought. Solid particles, presumably the remnants of the star-formation process, orbit around Vega and other stars and may provide the raw material for planetary systems. Emission from cool interstellar material has been traced throughout the Galaxy all the way to the galactic poles. Both the clumpiness and breadth of the distribution of this material were previously unsuspected. The far-infrared sky away from the galactic plane has been found to be dominated by spiral galaxies, some of which emit more than 50 percent and as much as 98 percent of their energy in the infrared-an exciting and surprising revelation. The IRAS mission is clearly the pathfinder for future missions that, to a large extent, will be devoted to the discoveries revealed by IRAS.

Jupiter's Spectrum Between 12 and 24 Micrometers.

Spectroscopic measurements of the thermal radiation from Jupiter between 12 and 24 micrometers (420 to 840 reciprocal centimeters) with a resolution of 4 reciprocal centimeters are used to infer the Jovian temperature structure in the pressure region 0.1 to 0.4 atmosphere. The brightness temperature spectrum is in good agreement with previous ground-based measurements between 11 and 13 micrometers and with airborne measurements between 18 and 25 micrometers. However, the integrated flux calculated for a filter window and viewing angle equivalent to those of the 20 micrometer channel of Pioneer 10 is 20 percent below that measured by the Pioneer infrared radiometer. The Q branch of the v(5) fundamental band of acetylene at 730 reciprocal centimeters appears in emission and leads to a mixing ratio estimate of 10(-6 +/- 0.5).

Infrared multidetector spectrometer for remote sensing of temperature profiles in the presence of clouds.

An infrared multidetector spectrometer with channels in the 4.3-microm and 15-microm CO(2) bands for the remote sensing of temperature profiles in the presence of clouds is described. Results obtained from aircraft flights in July 1975 over ocean sites under various conditions of cloudiness demonstrate the capability of the dual frequency technique to recover surface temperatures to an accuracy of +/-0.5 K in the presence of up to 90% cloud cover.