Ancillary observations for a first echo study: five million antenna camera digital images

An antenna-mounted camera system was installed on the NCAR/EOL S-PolKa radar for the RICO experiment. RICO (Rain In Cumulus over the Ocean) was, in part, an experiment to study the formation of rain in shallow cumulus over the undisturbed ocean. S-PolKa, a dual frequency (S-band and Ka band) polarimetric radar, was fielded on the island of Barbuda, the north-eastern most island in the Antilles chain. S-PolKa had an unobstructed view in all directions out to a range of ~150 km over the open ocean. S-PolKa's role was to establish a climatology of rain clouds for the region, and to study the time-to-formation of first precipitation from that region's small cumulus.

As part of “first echo” studies, it was required that S-PolKa be outfitted with an antenna-mounted camera. In the past, analog video cameras have been infrequently used in such a capacity, producing adequate but not optimal results. Image quality was often impacted by electronic interference, images were of only video quality, and linkage of images to particular times and scan directions was labor intensive.

Described here is the digital camera system that was installed on S-PolKa as an aid to RICO's first echo studies. Additionally, a simple image review package is demonstrated, allowing the user to quickly select particular images for review.

The camera used was a commercial webcam producing a progressive-scan color image with high resolution and very good contrast. The chosen camera had an extremely high lux rating, allowing the camera to remain in place even during programmed radar scans of the solar disk. The camera was enclosed in a weather-proof housing and used wireless Ethernet to transfer images to a computer in the operations van. Even with these requirements, camera cost was very reasonable. The review software allows a user to select images based upon time, or azimuth angle, or through links established in a table of volume scans. Linked to the antenna camera images are radar images from the same time period. The review system is designed to be web-based, but practical bandwidth considerations require that images be available on a local host for rapid review of images. Images reviewed are the full resolution, unprocessed JPEG images collected by the camera in real-time. Images were logged every half second, with over five million high-quality images (~120 GBytes) logged over the 65-day course of the RICO experiment.