Instruments

 The Daedalus 1268 airborne thematic mapper

The Daedalus 1268 Airborne Thematic Mapper (ATM) collects radiation from the Earth’s surface in 11 different bandwidths, in the visible, near infrared and thermal bands of the ems. The scanner is a passive remote sensing device, and is designed for use on an airborne platform. It operates by using a rotating scan mirror to capture the radiated light, with both visible and near infrared being split and then imaged onto a number of silicon detectors. The middle infrared and thermal radiation is dealt with slightly differently, as they are split and then recorded onto three single detector elements, which are enclosed within liquid nitrogen cooled containers (see the image below which shows the scanner uncovered).

 Bands one to five collect data in the visible part of the spectrum, with bands six to eight in the near infrared, bands nine and ten in the short-wave infrared, and bands eleven and twelve in the same mid infra-red or thermal wavelength, but with channel 12 collected using half the gain setting, thus utilising a different radiometric sensitivity to help alleviate any potential over-exposure problems (only applicable to the data collected in 1992, as updates to the scanner have to a large extent dealt with this problem).

 The scan mirror can be set to three different synchronised speeds (12.5, 25 and 50 Hz), so that data collection at different altitudes can be linked to ground coverage. In order to avoid any gaps in the area coverage along the flight lines, around a 10% overlap between alternate scanlines is employed. The ground resolution of multispectral data is both altitude and airspeed dependent.

 Compact Airborne Spectrographic Imager (CASI) data

The system used is a CASI-2, made by Itres Research of Canada, and uses a two dimensional CCD array imaging spectrograph. It utilises a pushbroom scanning mode, with the full swath width (54.4 degrees field of view) imaged simultaneously over a large number of spectral bands (up to as many as 288 in hyperspectral mode), between the visible and near infra-red areas of the electro magnetic spectrum (between 405 and 950nm). The resolution of the data varies depending on both altitude and the number of bands being collected. For the 2005 data flight, 48 bands were collected at a height of 800 metres, giving a nominal resolution of around 1.5 metres per pixel. This is the same nominal ground resolution as that collected by both the 1992 Daedalus 1268 flight and the 2005 Daedalus flight, so all three of the multi spectral datasets could be directly compared, at least in terms of their respective ground resolutions.

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