DEM: errors and the Topographic effect Review note: Photogrammetric DEMs are DTMs – bare earth Satellite DEMs are mostly DSMs .. They differ by vegetation height (and other errors) Interpolation / accuracy / scale / resampling

SRTM comparison with topographic DEM http://gisweb.ciat.cgiar.org/sig/download/laboratory_gis/srtm_vs_topomap.pdf

TRIM DEM: PG (vertical accuracy 10 metres)

TRIM DEM – masspoints ~70m spacing captured onscreen from stereo-photography ‘soft copy’ (prior to fully automated image matching)

BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace.ca or lrdw.ca

Assiniboine Spillway, MB http://www.gov.mb.ca/stem/mrd/geo/demsm/metadata.html

SRTM – ASTER comparison Sample area in Indonesia

Bowron Lakes: 5,4,3 composite: the ‘topographic effect’

Avalanche slopes : 25-45°

Avalanche slopes : 25-45° Low vegetation cover http://gis.unbc.ca/courses/geog432/projects/2002/whiteet/index.htm

Compensating for the topographic effect Include DEM channels in classification e.g. elevation, slope, incidence 2. Include new channels that are topographically reduced: band ratios, PCA, Tasseled Cap, Indices 3. Use the DEM to adjust the image DNs e.g. cosine correction

Band ratios reduce topographic effect (shadow) Image DNs may be composed of three elements: atmospheric interference (e.g. haze) b. Illumination (angle of reflection) c. Albedo (responding to surface cover) ratios can reduce the effect of illumination from topography and highlight the differences in surface cover.

Brightness, greenness and wetness tasseled cap channels Generated by Principal Components Analysis (PCA) and Tasseled Cap (Tassel)

Kuzera, Rogan and Eastman (2005): http://www. geog. ucsb

DEMs Lab review: Correction operations require metadata, in this case: Sun azimuth ~ 151.59 Sun angle ~ 45.95

Generate Tasseled Cap Brightness and Greenness Use change vector analysis or classify by change in the two components Brightness Greenness

DEM differencing with landslides http://www.csrsr.ncu.edu.tw/08CSRWeb/ChinVer/C7Info/2010RSDMM/PPTpdf/3.pdf

Lloyd George outlet glacier, August 2005 (by guide outfitters)

Lloyd George Icefield LIA 1850 - red TRIM 1986 – green Landsat 2001- yellow

Comparison of DEMs for glaciers in the Himalayas

This is a close up of the DEM and with extents of the ASTER scenes I’ll be spending most of the talk considering glaciers in the Coast Mountains here shown with colors denoting elevations and superimposed on the TRIM DEM with illumination from the northwest. Many of these ice files

ASTER imagery 2000 SRTM – TRIM 2000-1987 Here is a closeup of Klinaklini glacier with the available NTDB ice extents and the extents that are provided by one of our research partners the BC government. It shows that changes in area for these larger glaciers is not always a good surrogate for changes in ice volume. However, we can use the contours from these older maps to produce former surfaces of these glaciers and develop DEMs using ASTER imagery. We can see from the upper right image that Klinaklini glacier Lost over 150 m near its terminus and that between 1970 and 2000 the glacier lost at least 8 cubic kilometers of ice. ASTER imagery 2000

(Homathko River Park) Result of subtraction of 2 DEMs TRIM - NTDB SRTM –TRIM SRTM - NTDB