of 14 bits and operates in the wavelength range of 3.0 - 5.0 μm. Cooling is provided by the on-board Stirling closed cycle cooler.
Imagery is provided by AITScan in two formats, JPEG and SAF (Standard Archive Format). The JPEG file format in not capable of storing original 14 bit data (maximum bit depth is 8 bit for the gray channel). SAF files, on the other hand, contain full 14 bit camera output (stored in 16 bit form for convenience), as well as camera calibration coefficients that are used to convert pixel values to temperature and radiance. The SAF file is, in essence, an archive, that stores a time series of imagery in the single-file form. This survey produced 24 SAF files, corresponding to the 24 flight lines. With each flight line consisting of approximately 250 separate images, the resulting dataset contains about 6,000 rasters.
2.3 Ground Data
In order to provide additional control over the results of the survey, ground-level temperature data was collected. A handheld infrared thermometer (“MT4 Minitemp” manufactured by RayTek) was used for ground-level temperature sampling. According to the manufacturer, the accuracy of “±2%, or ±1.7°C, whichever is greater,” can be achieved. Previous to taking any measurements, this thermometer was tested and calibrated in a laboratory setup, as illustrated by Figure 2
A cup of cold water (around 1°C) was set up on a heater. A magnetic mixer at the bottom of the cup was constantly rotated by the magnetic field created by heater. The heater was turned on and as the temperature rose, simultaneous measurements were taken by the infrared and calibrated alcohol thermometer. Measurements were taken until the water reached 21°C. Then, the difference between two sets of temperatures was calculated. The differences were normally distributed with a mean of 0.4°C and standard deviation of 0.16. This test demonstrated that in the temperature range of 5°C to 20°C the accuracy was approximately ±0.3°C.
A number of random temperature measurements were taken around the campus, using GPS to record their positions. In addition to these samples, two reference targets - two sheets of plywood, 2.5 by 1.2 m, covered in black matte paint - were set up two hours before the start of the survey, approximately 1 m above the ground level, as far from expected sources of thermal pollution as possible [8
]. These reference targets were later used in two different ways. First, both targets were used together with other ground samples to verify the pixel to radiance/temperature conversion model. In case the GPS positioning error would be too high to reliably identify the ground samples on the thermal imagery, two plywood targets would be a fall-back option to get at least some data for the model verification. Based on the proposed spatial resolution of 0.29 m, the size of the targets used would be enough for an accurate visual location. Second, the plywood targets were used to investigate the change of the temperature of the exposed objects overnight, if any. The sampling period was selected to match the data collection interval of the on-campus meteorology station.
Data from the on-campus automatic meteorology station located on the rooftop of the Latham Hall were collected every 30 minutes and contained temperature, pressure, and relative humidity values. Data on wind direction and speed were obtained from the nearby (6 km) meteorology station in Waterloo, Iowa. Throughout the night, the ambient air temperature stayed close to -6 °C, with humidity of 79%. Wind direction and speed were stable for the whole time of the survey (330°, 8 m/s). Except for the wind speed, meteorological conditions were favorable for the thermal infrared survey – clear sky, low ambient temperatures and absence of precipitation all benefit thermal contrast [6
2.4 GIS Data
Thermal imagery requires significant amount of processing. Automated means of analysis must be found in order to fully employ the benefits of remote sensing approach. Using GPS coordinates as a spatial reference, ground control samples were transformed into a sh