Realities of Satellite Interpretation (The things that will drive you crazy!)

1. Realities of Satellite Interpretation(The things that will drive you crazy!) Rachel M.K. Headley, PhD USGS Landsat Project

2. Interpretation Challenges • Very different land use or land cover types will look the same to the sensor. • There is no “forest” button.  • Applies to Supervised and Unsupervised classification • The same land cover or land use type can be classified as unique. • Geography matters! • Context of the image will give clues to solving above mysteries (mostly). • Recognize where you cannot overcome limitations.

3. 6 May 2007

4. Confused classification • Central PA, 6 May 2007 • Golf courses & early green fields • Deciduous forest & bare fields • Coniferous forest more distinct

5. 24 May 2007

6. Confused classification • Near Seattle, 14 May 2007 • Definition of “forest” important • Both Deciduous and Coniferous forests here • Notice the power line cut. • Aspect, slope, sun inclination • Different shadowing can result ‘false’ interpretation • Clearcut looks the same as ag field or developed • Here ag fields & developed lands are on a much smaller scale than timber harvesting. • Density of trees – what do you do with clearcut regrowth?

7. 14 May 2007

8. Confused classification • Southern Missouri, 24 May 2007 • Much greener than previous images – seasonality must be taken into account. • Deciduous is nearly indiscernible from green ag fields. • Are different colors of green different forest types – do you care? • Wet ag fields – what do you call them? • Different signature in bare ag fields.

9. 16 May 2007

10. Confused classification • Yellowstone, 16 May 2007 • Nearly same date as all previous scenes • Same band combination • Higher latitude and elevation = winter scene • Worthless for interpretation! • (Gorgeous though it may be)

11. 15 May 2007 5,4,3

12. 15 May 2007 7,5,2

13. Confused classification • Northern Virginia, 15 May 2007 • Different bands can tell different stories • Recommendation: create classifications with all bands, except thermal (and pan on L7). • All green things will be confused with each other in 5,4,3. 7,5,2 gives you much more distinction. • 7,5,2 makes bright things too bright. 5,4,3 gives better distinction. • Recommendation: Pick a different date for this area! • Too far into the growing season • Note: Mines: can be mixture of bare soil and water • Regionally dependent

14. Know what questions you’re asking • Be clever about choosing images • Know what types of land use or land cover you care about • Winter (leaf off): not useful • Early spring: target early greenup • Crop types & forest types (general) • Peak of green • Max NDVI, clear cuts, barren lands • Late fall: target post-harvest • Crop fields from forests

15. Geography Matters • Changes between years • Similar seasonality • Same dates don’t always work (take 2008) • Know your geography • Rules change • Seasonality • Interpretation • Land cover or land use types • Scale of change • Type of change • Completely unknown study area is doable, but difficult