TARFOX Abstracts
at AGU Special Sessions
Baltimore, MD, 5/29-30, 1997

Joseph M. Ritter (University of Miami, Coral Gables, Fl. 33146; 305-284-2325x3; e-mail:Ritter@phyvax.ir.miami.edu);
Kenneth J. Voss (University of Miami, Coral Gables, Fl. 33146; 305-284-2323x2; e-mail:KVoss@umiami.miami.edu);
Howard R. Gordon (University of Miami, Coral Gables, Fl. 33146; 305-284-2323xl; email:Gordon@phyvax.ir.miami.edu)

Radiometric measurements of the solar aureole when combined with spectral extinction data can yield data products such as aerosol size distributions and aerosol phase functions for small scattering angles. Ship motion coupled with large changes in aureole radiance over small angles require an instrument with a high signal to noise ratio, accurate pointing, fast triggering, short exposure times, low jitter, as well as sensor stability. An imaging radiometer which meets these requirements has been developed, and was deployed on a ship during the NASA TARFOX experiment.

The system consists of a cooled 512x512 CCD array, a 35 mm lens and filter wheel, an internal and external cooling system, sun alignment sensor and optics with associated triggering and digitizing electronics. This package is mounted on a 2m pole and pointed manually toward the sun. An occulter 140 cm from the camera aperture consisting of a 2.5 cm diameter ND5 filter attenuates the direct sunlight prohibiting internal flair while allowing for direct solar spectral extinction measurements simultaneous with optical scattering measurements. A sun alignment sensor automatically exposes the CCD when the camera orientation is correct. Control and data acquisition are performed by a desktop computer.

A thermoelectrically cooled CCD array provides a S/N of 10⁴. A computer controlled integration and shuttering system insures low integration time jitter(<.05%) while exposing rapidly enough (19 mSec) to insure no image blur due to ship motion. The instrument has an angular resolution of .05 degrees and a circular field of view of +/- 7.5 degrees corresponding to .054 steradians centered on the sun. Individual wavelength measurements are accomplished using 10 nm interference filters centered at 440, 560, 670 and 860 nm. The instrument allows measurement of small angle optical scattering within 1 degree of the edge of the solar disk even when deployed on an unstable platform such as a ship.