The camera used during Leg 201 was a ThermaCam SC 2000 camera, made by FLIR Systems. This camera measures temperatures from -40°C to +1500°C. For onboard application, it was set to record a range of temperatures from -40°C to +120°C (range 1). The precision of this camera is 0.1°C at 30°C and the accuracy is ±2°C. However, emissivity corrections can improve the accuracy to 0.0°C (R. Rogers, pers. comm., 2002 [N1]).
In order to achieve the most accurate temperature measurements, the emissivity of the core liner was established by placing a piece of electrical tape (with a known emissivity of 0.95) on the core liner. The apparent temperatures of the tape and the core liner were compared, and the emissivity of the core liner was determined to be 0.95 (tape was not visible on the core liner with the IR camera). Polycarbonate tubing is opaque to infrared radiation, so the remaining radiation was attributed to reflection. All analyses were conducted with the emissivity set at 0.95.
The camera was mounted on a wheeled cart (Fig. F1) to maintain constant distance between the camera and core liner and rolled across each core before any other sampling was conducted on the catwalk. A dedicated lap-top computer recorded the camera images at a rate of 5 frames/s. An external screen attached to the camera showed a range of temperatures from 15° to 25°C. This allowed immediate identification of cold spots, which were then visually and/or chemically inspected for evidence of hydrate. A depth scale was established in order to correlate the hydrate identified by the camera with other physical properties, chemical properties, and visual observations of hydrate. This was done by assigning the curated depth to the first image, then dividing the total core length by the number of images. Then a depth was incrementally assigned to each image. There were typically 200-300 images for each core. The images were analyzed with FLIR ThermaCam Researcher software. An analysis box was hand selected in the first image of the sequence file and was placed to avoid areas of significant reflection or other interference. The sequence file was played from beginning to end, and the maximum, minimum, and average temperatures from the analysis box were extracted from each image. All temperatures presented are minimum temperatures to highlight negative temperature anomalies. Further details of camera setup and data analysis procedures are available in "Infrared Thermal Imaging" in "Physical Properties" in the "Explanatory Notes" chapter.
Scans at Sites 1226 and 1230 were used for comparison between a nonhydrate-bearing site and a hydrate-bearing site, respectively.
Air temperature data were recorded by the officers of the ship's bridge every 4 hr. The thermometer was located in a weather box adjacent to the bridge, ~50 ft away from the catwalk where the cores were imaged.