Summary of image metadata items

The image metadata schema describes two basic types of image metadata items: global ( i.e., applies the image as a whole) and band-specific.

The global metadata items specify the following:

a textual data set description
number of image bands
number of radiometric transformations in the sequence of radiometric transformations stored in the band-specific metadata
name of the sensor model (optional)
name of the sensor type (optional)
nominal location of image acquisition (optional)
nominal time of image acquisition (optional)
nominal heading of the platform (optional)
fore-aft tilt of the sensor relative to the gravity vector (optional)
total field-of-view of the sensor (optional)

The nominal location, time, and heading apply to the full image extent, and are intended to be used to calculate a solar illumination direction relative to the image raster and to support atmospheric correction calculations.

The band-specific metadata items specify the following:

band ID number
number of the file channel that stores the band
band quality (optional)
response profile (optional)
radiometric transformation sequence (optional)

The band quality value allows certain bands to be excluded from plots of band value versus wavelength, or from processing.

Bands with a quality value of either plot or bmask are considered to be valid in the sense that their values should not be excluded from plotting or processing on the basis of noise content (but the user is not prevented from omitting such bands from a user-defined band selection that is based on wavelength or storage channel).

Bands with a quality value of either skip or mask are excluded from processing if the user indicates in the program parameters that only valid bands are to be processed. Also, the values for such bands are not plotted: plots are drawn with linearly interpolated values (based on the bracketing valid bands) at skip-band wavelengths, and with gaps at mask-band wavelengths.

Bands with a mask quality value are commonly removed from the data set. A valid band that immediately preceeds a mask band has a bmask (for "begin mask") quality value. When mask bands are removed, remaining bmask bands indicate where the removal occurred.

The band response profile has three parameters that are given in the metadata: type (one of box, triangular, or gaussian), center wavelength value in nanometres, and a full-width at half-maximum (FWHM) in nanometres. The Hyperspectral Analysis Package programs use the band response profiles in resampling spectra.

The radiometric transformation sequence consists of a sequence of one or more (quantity, gain, offset) triplets. The quantity value labels the physical type of the transformation output at that place in the sequence: adj_no_units for "adjusted but no physical units," apprad for "apparent, (i.e., "at-sensor") radiance," scrad for "scene radiance," scirrad for "scene irradiance," and refl for "reflectance".

Metadata on the image row and column dimensions, pixel value datatype, and interleaving are assumed to be held in the channel headers of the PCIDSK file that contains the image.