Information Session: October 12, 2011 – 2:30 – 4:00 in Rm. 7-150

Interdisciplinary Field School to Peru June 2012 For information, contact: Dr. Catherine Nolin (nolin@unbc.ca) or Scott Emmons (emmons@unbc.ca) 2

Digital Elevation Models (DEM) / DTM Uses in remote sensing: queries and analysis, 3D visualisation, layers in classification, Fogo Island, Cape Verde Republic ASTER DEM / image Banks Peninsula, Christchurch, New Zealand

DEM sources – where do they come from ? Almost all DEMs have been created from remote sensing: a. DEMs from digitising contours (e.g. NTDB) The earliest were created by digitising contours on maps into layers stereo photos -> contour lines -> digitised lines -> interpolate to raster grid Arcmap: topo 2 raster PCI geomatica: vdemint

DEM data sources b. Digital Stereo photogrammetry: (e.g. BC TRIM) Mass points captured from aerial photographs stereo photos -> mass points -> interpolate to raster grid

TRIM DEM – masspoints ~70m spacing captured onscreen from stereo-photography ‘soft copy’ Created from mass points and break lines Aerial Photography 1979-89 (1:70,000)

BC TRIM DEM Interpolated to 25m grid By 1:250,000 map sheets (100 tiles assembled together) Vertical accuracy to within 10m 16 bit codes, -9999 for invalid numbers e.g. across border into AB

BC TRIM DEM 25m raster grid Created from mass points and break lines Aerial Photography 1979-89 (1:70,000)

Post 2000 methods c. Direct image grid DEM data from imagery RADAR e.g. Shuttle Radar Topographic Mission (SRTM) Stereo digital satellite imagery (adjacent satellite tracks) Issues: cloud cover and missing data ASTER SPOT

DEM - layers a. Elevation DN = (metres, 16 bit):  represented as grayscale or pseudocolour tints; DEMs are stored as integer elevations (metres) or 32 bit (after interpolation) some (NTS) DEM tiles in Canada may still be in feet (how would the values compare ?) …. conversion = .3048

b. Shaded relief (hillshade) A cartographic layer, DN= 0 - 255 (relative amount of light reflected), as grayscale; light source can be selected, usually from the NW. High values on NW facing slopes, low values on SE facing slopes. Select light source azimuth and angle Default = 315, 45 useful for detecting errors and assessing quality

DEM grid displayed as grayscale Hillshading (NW light source – 315, 45)

BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace BC provincial DEM 1985 (1981-1989) – Homathko Icefield - mapplace.ca or lrdw.ca Errors from lack of contrast in snowfields = few data mass points

1 metre hillshaded DEM … from contours

c. Slope Calculated in degrees (0-90) or % (0 -> infinity) slope is rise/run = vertical change over the horizontal distance 8 bit results should be adequate for most purposes

4. Aspect The direction in which a slope is facing, measured by azimuth (0-360) This raises three questions for analysis: north facing slope has both extreme values, 0 and 360 ****** flat slopes have no value (they are given an arbitrary numerical value, e.g. 555) 0-360 requires 16 bit data; some software (PCI) converts to 8 bit by dividing by 2

5. Incidence Image data look similar to shaded relief, but with values 0-90 the angle (degree) of light incidence, based on the sun position at time of scene capture. Requires knowledge of sun elevation and azimuth for the scene = metadata

6. Second derivatives: slope concavity and convexity, used in generating watersheds and also viewsheds using line of sight

7. 3D perspectives / fly-throughs e.g. Google Earth etc..

8. Anaglyphs St-Pierre – Miquelon SRTM DEM

Klinakline Glacier, south Coast Mountains (ASTER DEM)

DEMs in Digital Image Classification Land Cover Classification Using IRS LISS III Image and DEM in a Rugged Terrain: A Case Study in Himalayas Green Red NIR MIR NDVI DEM http://www.geocarto.com.hk/cgi-bin/pages1/june05/33_Saha.pdf

Next lecture: DEMs available A DEM is a continuous grid of elevation values – one height value per pixel ….. in a channel (not a band) AGENCY  SCALE  RESOLUTION (metres) Municipal  1: 2,000 1  Provincial  1: 20,000  25  Federal  1: 50,000 50  Federal  1: 250,000  200  Global  1: 1,000,000  500-1000  Download Canadian data from geobase.ca (1:50,000 / 1:25,000) * BC is provincial data (25m) resampled for NTDB (50m)