1. CS 128/ES 228 - Lecture 9b1 Photogrammetry & Image Analysis

2. CS 128/ES 228 - Lecture 9b2 Photogrammetry Originally, the science (or art?) of interpreting aerial photographs Stress on quantitative measurements Now includes analysis of digital images from many sources Image from Avery. Interpretation of Aerial Photographs.

3. CS 128/ES 228 - Lecture 9b3 A hierarchy of remote sensing Satellite sensing Aerial photography Ground-truthing Image from Avery. Interpretation of Aerial Photographs.

4. CS 128/ES 228 - Lecture 9b4 Perspectives Vertical: - orthogonal perspective - planimetric map data Oblique: - high oblique (includes horizon) - low oblique (no horizon) Image from Avery. Interpretation of Aerial Photographs.

5. CS 128/ES 228 - Lecture 9b5 Scale Determine from: Plane altitude RF = lens focal length altitude of plane Known ground features Top image from Avery. Interpretation of Aerial Photographs. Bottom images from Ben Meadows catalog (L), Olean NW DOQQ ®

6. CS 128/ES 228 - Lecture 9b6 Problems Plane altitude determining altitude (barometer, radar altimeter) variation among photos uneven terrain Known ground features: need objects of known size & large enough for accurate measurement, or pair of points for distance measure

7. CS 128/ES 228 - Lecture 9b7 Planimetric view Perfectly vertical (orthogonal) perspective All features in correct horizontal positions Impossible unless at infinite height

8. CS 128/ES 228 - Lecture 9b8 The principle point Point directly under camera lens (‘nadir’) Elevated objects lean away from PP Depressed objects lean toward PP Causes image displacement Images from Avery. Interpretation of Aerial Photographs.

9. CS 128/ES 228 - Lecture 9b9 Vertical relief causes displacement Transmission line is straight - why does the line appear straight in one photo and jagged in second? In left stereogram, line is ~ on nadir; in right stereogram, far from nadir Image from Avery. Interpretation of Aerial Photographs.

10. CS 128/ES 228 - Lecture 9b10 Image displacement: Source of error in horizontal locations, but Permits estimation of feature elevations stereoscopic parallax Image from Avery. Interpretation of Aerial Photographs.

11. CS 128/ES 228 - Lecture 9b11 Stereoscopic photo pairs Image from Avery. Interpretation of Aerial Photographs.

12. CS 128/ES 228 - Lecture 9b12 Stereoscopes need pair of overlapping photos different principle points results in parallax used to create topographic contours

13. CS 128/ES 228 - Lecture 9b13 Shadows Need sun angle Object must be vertical Shadow must come from top and fall on level ground H = L x tan(α) Image from Avery. Interpretation of Aerial Photographs.\

14. CS 128/ES 228 - Lecture 9b14 Rectification of aerial photographs Rectification: process of geometric correction that turns an aerial photograph into a planimetric (map-like) image Problems: lens distortion Earth curvature camera tilt terrain relief

15. CS 128/ES 228 - Lecture 9b15 Rectification process 1.Scan aerial photograph at high resolution 2.Locate ground control points on scanned image: ≥3 for affine transformation ≥5 for rubbersheeting 3.Combine with DEM to correct relief displacement 4.Rectify to a ground coordinate system

16. CS 128/ES 228 - Lecture 9b16 Relief distortion Objects at different distances form the lens will be distorted

17. CS 128/ES 228 - Lecture 9b17 Result: digital orthophotograph USGS supplies in DOQ format NYS GIS site provides free colored infrared DOQQs

18. CS 128/ES 228 - Lecture 9b18 Urban areas: building tilt In urban areas, tall buildings seem to lean toward the principal point of the photograph Corrected by building a DTM of each building Permits virtual reality “flyovers” Thorpe, A. Digital orthophotography in New York City. www.sanborn.com/Pdfs/Article_DOI_Thorpe.pdf

19. CS 128/ES 228 - Lecture 9b19 Image Analysis Identification of objects Assigning attributes to objects or areas Assessing the significance of patterns Can be:  Visual interpretation  Computer-assisted image analysis

20. CS 128/ES 228 - Lecture 9b20 Landsat Images Landsat 1-4 launched 1972 – ’82; expired Landsat 5 & 7 launched 1985 & 1999; both operational TM: thematic mapper. - 7 spectral bands - designed primarily for ES themes http://landsat.gsfc.nasa.gov/project/L7images.html

21. CS 128/ES 228 - Lecture 9b21 TM Applications BandSpectral range (µm) “Color”Application 10.45 – 0.52Blue-greenSoil/vegetation separation 20.52 – 0.60GreenReflection from vegetation 30.63 – 0.69RedChlorophyll absorption 40.76 – 0.90Near IRDelineation of water bodies 51.55 – 1.75Mid IRVegetative moisture 610.4 – 12.5Far IRHydrothermal mapping 72.08 – 2.35Mid IRPlant heat stress

22. CS 128/ES 228 - Lecture 9b22 Hydrology example Images from Avery. Interpretation of Aerial Photographs.

23. CS 128/ES 228 - Lecture 9b23 Terra (and EOS) Terra launched Carries 5 instruments; the MSS imager is called ASTER (from Japan) 14 spectral bands: - 3 VIS/near IR (15 m) - 6 short IR (30 m) - 5 thermal IR (90 m) Images from www.nasa.gov

24. CS 128/ES 228 - Lecture 9b24 ASTER spectral signature library “Welcome to the ASTER spectral library, a compilation of almost 2000 spectra of natural and man made materials.”ASTER http://speclib.jpl.nasa.gov

25. CS 128/ES 228 - Lecture 9b25 Classification schemes 1.a Unsupervised: raw data analyzed for clusters 1.b Supervised: prior categories imposed 2. Classification of new data 3. Ground truthing … Lo & Yeung. Concepts and Techniques of Geographic Information Systems

26. CS 128/ES 228 - Lecture 9b26 And that’s the fun part …