Lower image unit weights
indicate more tightly controlled model solutions. DEMs were
processed from each of the model solutions at 10m post
spacing using a triangular irregular network (TIN) data structure
and an adaptive terrain extraction matching algorithm
(using SocetSet software, BAE Systems), and were validated
by calculating elevation residuals between each GPS check
point and its spatially coincident DEM cell value.
We investigated the effects of different GCP configurations
on DEM error by differencing each lidar point-controlled
photogrammetric DEM (summer 2003) from a DEM derived
solely from the lidar data. This gave a straightforward qualitycontrol
test whereby differences closest to zero represented
the best-quality DEM surfaces. We also examined the effects
of GCP configurations on estimates of glacier volume change
by computing differences between photogrammetric DEMs
(summer 2003) and a DEM derived from repeat survey
lidar data from summer 2005, and