The Airborne Thematic Mapper (ATM)
The scan head of the Daedalus 1268 ATM
The Daedalus (now ArgonST
)
1268 ATM is a passive multispectral scanner providing 11 fixed wavelength
position bands in the visible, near, short and thermal infrared. The ATM
was purchased by NERC in 1993. The bands approximate those of Landsat (see
bandwidth diagram).
| Channel | Wavelength (mm) |
|---|---|
| 1 | 0.42-0.45 |
| 2 | 0.45-0.52 |
| 3 | 0.52-0.60 |
| 4 | 0.60-0.62 |
| 5 | 0.63-0.69 |
| 6 | 0.69-0.75 |
| 7 | 0.76-0.90 |
| 8 | 0.91-1.05 |
| 9 | 1.55-1.75 |
| 10 | 2.08-2.35 |
| 11 | 8.5-13.0 |
The ARSF ATM represents a significant upgrade and enhancement of the original Daedalus sensor. New electronics provide 16-bit Analogue to Digital conversion with up to 65,536 digital intensity levels and increased Signal to Noise, with flexible data recording on removable hard drives.
| Instantaneous Field Of View | 2.5 mrad |
|---|---|
| Pixel swath | 938 |
| Digitised Field of View | 90° |
| Scan Rate | 12.5 , 25 and 50 Hz |
| Radiometric Resolution | 16 bit |
| Temperature Reference | Two black-bodies for calibration of thermal channel |
Ground Spatial Resolution
The ground spatial resolution (pixel size) of the Airborne Thematic Mapper (ATM) is defined both by the optical characteristics of the scan head, which provides an Instantaneous Field of View (IFOV), and the aircraft altitude. Pixel length and pixel width are both defined by this IFOV, but ground dimensions will vary differently as a function of the scan angle away from nadir. Exact sample spacing on the ground will also be dependent on the attitude of the aircraft and altitude, so can only be calculated in combination with output from the navigation information which is supplied with the data. The scan geometry is further complicated by the forward motion of the aircraft during the scan mirror rotation since adjacent pixel centres will advance as the aircraft moves forward during a scanline. However, the short time required for the signal integration of an individual pixel means that there is negligible smearing of the pixel and the pixel length is dominated by the IFOV.