Airborne Infrared Imagery during CBLAST-LOW 2003

Christopher J. Zappa

Woods Hole Oceanographic Institution

&

Andrew T. Jessup

Applied Physics Laboratory/University of Washington

Figure 1. Cessna Skymaster chartered for CBLAST-LOW 2003 through Ambroult Aviation based in Chatham, MA.

Airborne measurements of sea surface temperature variability using infrared (IR) imagery are being made during the CBLAST-LOW activities for 2003. The IR equipment is installed aboard a Cessna Skymaster (see Figure 1) operated by Ambroult Aviation based in Chatham, MA. The system consists of a downward-looking longwave IR imager that has an image size of 512 x 640, a collocated downward-looking video camera, and a collocated downward-looking, longwave, narrow field-of-view (FOV) IR radiometer (see Figure 2). Nominally, the plane flies at an altitude of 850 m but will fly as low as 300 m. These altitudes correspond to a resolution for the imager of roughly 0.8 m and 0.3 m, respectively. The system includes a uniform target blackbody for the calibration and non-uniformity correction of the QWIP array detector (see Figure 3). The QWIP array performance allowed for the determination of temperature variability of less than 20 mK. The system also includes a second longwave infrared imager that is directed skyward as well as a narrow FOV radiometer to complement the downward instruments (see Figure 4). The upward-looking instrumentation will be used to discriminate real from apparent ocean surface temperature variability. Apparent temperature variability in the infrared imagery may arise on partly cloudy days when both the radiatively-cold sky and radiatively-warm clouds reflect into the imager FOV. The aircraft was also installed with a 4-receiver GPS system to provide accurate information of the aircraft flight performance such as its speed, course, heading, pitch, roll, and altitude.

The Cessna Skymaster has enough room for the system as well as an instrument operator in addition to the pilot. An onboard operator allows for the calibration and maintenance of the system instrumentation, real-time data quality control, a greater ability to probe interesting features as per the operator’s discretion, and the ability to make adjustments in the flight plan in accordance with these features. The standard flight plan was a “mowing the lawn” pattern that encompassed the CBLAST-LOW region south of Martha’s Vineyard and included the Heavy mooring sites, the Light Mooring sites, and the Air-Sea Interaction Tower (ASIT) (see Figure 5).

Figure 2. Picture on the left is a close-up of the cargo door on the Cessna Skymaster that was modified to accommodate our downward-looking instruments. Picture on the right is a close-up of the downward-looking infrared imager, collocated video camera, and collocated, narrow FOV infrared radiometer.

Figure 3. Pictures of the downward-looking infrared imager in (left) the operation position looking at the ocean surface and in (right) the calibration mode position looking at the uniform target blackbody.

Figure 4. Picture taken inside the Cessna Skymaster showing the upward-looking infrared imager and narrow FOV radiometer that complement the downward-looking instrumentation. The picture was taken from the pilot’s seat on the port side of the aircraft and the view is towards the back of the cabin. The operator seat was installed on the port side of the cabin behind the pilot seat.

Figure 5. Plot of the standard “mowing the lawn” flight track pattern flown during the CBLAST-LOW summer 2003 activities that included the Heavy mooring sites, the Light Mooring sites, and the Air-Sea Interaction Tower (ASIT).