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

Interpretation Challenges  Very different land use or land cover types will look the same to the sensor. –There is no “forest” button. –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.

6 May 2007

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

24 May 2007

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?

14 May 2007

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.

16 May 2007

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)

15 May ,4,3

15 May ,5,2

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

 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

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