Photometry

Single pointing mode

1. PHT05:
   Absolute Photometry from =3.2 to 120 m using PHT-P detectors. An accurate observation is performed of the total sky flux within a given aperture. A reference level is obtained and absolute flux calibration is achieved by a staring measurement of the internal fine calibration source (FCS). The user selects one filter and one aperture.

   An optional dark measurement can be selected for determination of the photometric zero point (signal for zero external illumination). Also an optional measurement against the cold FCS can be selected in order to determine the contamination of the FCS signal by external straylight (see Section 6.4). This is the only AOT type which offers these options.

   Chopping or raster mode are not possible.

   Scientific application: absolute sky brightness photometry on large extended sources, e.g. zodiacal light, galactic background emission, extragalactic background emission.

2. PHT25:
   Absolute Photometry - long wavelength analogue of AOT PHT05 from =40 to 240 m using PHT-C detectors. No apertures are required as the field of view is determined by the solid angle of the detector arrays.