The primary components of the HARLS-CS
are geometrically and, except in the case of the laser scanner, radiometrically
calibrated on a regular basis. The manufacturers of the imaging components,
Nikon and Duncan, provide radiometric calibration reports upon delivery
and publish well-documented guidelines for subsequent calibration. Because
neither the DS100 nor the MS4100 are considered "metric" cameras, geometric
calibration of these sensors will make use of a three-dimensional target
array, maintained at CAST, and "self-calibrating bundle adjustment"
software (Clarke, et al, 1998). Both sensors can thus be characterized
by the alignment and size of their sensor arrays and the distortion
caused by the lens systems. The Optech laser profiler may be geometrically
calibrated using similar techniques. Integration of the primary components
into a coherent multi-source sensor requires accurate knowledge of the
relative position of the components during data collection to ensure
that the various observations made by each instrument can be related
to a particular point in space. This is accomplished using "in-the-field"
techniques that position and orient each component relative to each
other as well as to the target. For example, the relative orientation
of the instruments might require observations of the sensors as well
as the target with the high precision total station and a subsequent
triangulation and/or trilateration to obtain information about their
relative positions. When absolute orientation is required (i.e. position
and orientation relative to a geodetic datum and/or projection), one
or more of the GPS units may be placed in the field of view of each
sensor and its position imaged along with the target.
