Abstract. Polar Ozone and Aerosol Measurement (POAM) III, a follow-on to the successful POAM II, is a spaceborne experiment designed to measure the vertical profiles of ozone, water vapor, nitrogen dioxide, and aerosol extinction in the polar stratosphere and upper troposphere with a vertical resolution of 1-2 km. Measurements are made by the solar occultation technique. POAM III, now in polar orbit aboard the SPOT 4 satellite, is providing data on north-and southpolar ozone phenomena, including the south-polar ozone hole, and on the spatial and temporal variability of stratospheric aerosols, polar stratospheric clouds, and polar mesospheric clouds.

The Hyperspectral Imager for the Coastal Ocean (HICO) is the first spaceborne hyperspectral sensor designed specifically for the coastal ocean and estuarial, riverine, or other shallow-water areas. The HICO generates hyperspectral images, primarily over the 400-900 nm spectral range, with a ground sample distance of ≈90 m (at nadir) and a high signal-to-noise ratio. The HICO is now operating on the International Space Station (ISS). Its cross-track and along-track fields of view are 42 km (at nadir) and 192 km, respectively, for a total scene area of 8000 km(2). The HICO is an innovative prototype sensor that builds on extensive experience with airborne sensors and makes extensive use of commercial off-the-shelf components to build a space sensor at a small fraction of the usual cost and time. Here we describe the instrument's design and characterization and present early images from the ISS.

The second Polar Ozone and Aerosol Measurement instrument (POAM II) is a spaceborne experiment designed to measure the vertical profiles of ozone, water vapor, nitrogen dioxide, aerosol extinction, and temperature in the polar stratosphere and upper troposphere with a vertical resolution of about i km. Measurements are made by the solar occultation technique. The instrument package, which has a mass of less than 25 kg, is carried on the Satellite Pour l'Observation de la Terre (SPOT) 3 spacecraft and has a design lifetime of 3-5 years. POAM II has provided data on the south polar ozone hole, north and south polar ozone phenomena, the spatial and temporal variability of stratospheric aerosols and polar stratospheric clouds, and has detected polar mesospheric clouds. IntroductionThe second Polar Ozone and Aerosol Measurement (POAM II) instrument is a nine-channel photometer designed to measure constituents and properties of the atmosphere that are critical for understanding ozone chemistry in the polar regions. The measured constituents and approximate altitude ranges are shown in Table 1. Measurements are made by the solar occultation technique [Russerr et at., 1993]: the Sun is observed through the Earth's atmosphere as it rises and sets, as seen from the satellite. These measurements are performed with an altitude accuracy of about 1 km and a vertical resolution of 0.8 km; the vertical resolution of the geophysical profiles inferred from the measurements is about 1 km. Horizontal resolution, as determined by the geometry of the line of sight (LOS) through the atmosphere and the angular size of the Sun, is about 200 km along the LOS and 30 km across it. Additionally, the LOS moves horizontally by about 100 km during the approximately 15 s it takes for the Sun to traverse the atmosphere. POAM II, funded by the Ballistic Missile Defense Organization, was launched on September 26, 1993, on the Satellite Pour l'Observation de la Terre (SPOT) 3 spacecraft and is performing successfully. The Naval Research Laboratory's POAM program is currently constructing two more instruments of this type, one for SPOT 4 and one for the fourth Space Test Experiment Platform (STEP 4; this satellite will not be in polar orbit). The basic POAM concept originated at the Department of Physics and Astronomy of the University of Wyoming, which built a three-channel, ozone-only version (POAM I). Unfortunately, the experiment failed immediately after launch in 1985. The SPOT 3 satellite is in a Sun-synchronous orbit at an altitude of 833 km, an inclination of 98.7 ø, and a period of 101.5 min; the descending node is crossed at 1030 LT. As seen from the satellite, the Sun rises in the north polar region and sets in the south polar region 14.2 times per day. This orbit makes SPOT 3 an excellent platform for polar ozone observations. From launch to late 1995, data have been gathered from approximately 14,000 solar occultation events, and preliminary scientific results have been presented on polar ozone phenomena in general and the formation and ...

In scan-mode synthetic aperture imaging radar, spatial resolution in a range is given by a frequency-swept waveform, whereas resolution in the orthogonal direction is derived from the record of phase as the beam footprint executes linear motion over the object. We demonstrate here what is to our knowledge the first two-dimensional imaging that uses exactly this process in the optical domain for a 1 cm x 1 cm object with 90 mumx170 mum resolution.

Errors in the estimated constituent concentrations in optically complex waters due solely to sensor noise in a spaceborne hyperspectral sensor can be as high as 80%. The goal of this work is to elucidate the effect of signal-to-noise ratio (SNR) on the accuracy of retrieved constituent concentrations. Large variations in the magnitude and spectral shape of the reflectances from coastal waters complicate the impact of SNR on the accuracy of estimation. Due to the low reflectance of water, the actual SNR encountered for a water target is usually quite lower than the prescribed SNR. The low SNR can be a significant source of error in the estimated constituent concentrations. Simulated and measured at-surface reflectances were used in this study. A radiative transfer code, Tafkaa, was used to propagate the at-surface reflectances up and down through the atmosphere. A sensor noise model based on that of the spaceborne hyperspectral sensor HICO was applied to the at-sensor radiances. Concentrations of chlorophyll-a, colored dissolved organic matter, and total suspended solids were estimated using an optimized error minimization approach and a few semi-analytical algorithms. Improving the SNR by reasonably modifying the sensor design can reduce estimation uncertainties by 10% or more.