Realities of Satellite Realities of Satellite InterpretationInterpretation

(The things that will drive you (The things that will drive you crazy!)crazy!)

Rachel M.K. Headley, PhDRachel M.K. Headley, PhD

USGS Landsat ProjectUSGS Landsat Project

Interpretation ChallengesInterpretation Challenges

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

Applies to Supervised and Unsupervised Applies to Supervised and Unsupervised classificationclassification

The same land cover or land use type can The same land cover or land use type can be classified as unique.be classified as unique.

Geography matters!Geography matters!– Context of the image will give clues to solving Context of the image will give clues to solving

above mysteries (mostly). above mysteries (mostly). Recognize where you cannot overcome Recognize where you cannot overcome

limitations.limitations.

6 May 2007

Confused classificationConfused classification

Central PA, 6 May 2007Central PA, 6 May 2007– Golf courses & early green fieldsGolf courses & early green fields– Deciduous forest & bare fieldsDeciduous forest & bare fields– Coniferous forest more distinctConiferous forest more distinct

24 May 2007

Confused classificationConfused classification

Near Seattle, 14 May 2007Near Seattle, 14 May 2007– Definition of “forest” importantDefinition of “forest” important

Both Deciduous and Coniferous forests hereBoth Deciduous and Coniferous forests here– Notice the power line cut.Notice the power line cut.

– Aspect, slope, sun inclinationAspect, slope, sun inclination Different shadowing can result ‘false’ interpretationDifferent shadowing can result ‘false’ interpretation

– Clearcut looks the same as ag field or developedClearcut looks the same as ag field or developed Here ag fields & developed lands are on a much Here ag fields & developed lands are on a much

smaller scale than timber harvesting.smaller scale than timber harvesting.

Density of trees – what do you do with Density of trees – what do you do with clearcut regrowth?clearcut regrowth?

14 May 2007

Confused classificationConfused classification

Southern Missouri, 24 May 2007Southern Missouri, 24 May 2007– Much greener than previous images – Much greener than previous images –

seasonality must be taken into account.seasonality must be taken into account.– Deciduous is nearly indiscernible from Deciduous is nearly indiscernible from

green ag fields.green ag fields.– Are different colors of green different Are different colors of green different

forest types – do you care?forest types – do you care?– Wet ag fields – what do you call them?Wet ag fields – what do you call them?– Different signature in bare ag fields.Different signature in bare ag fields.

16 May 2007

Confused classificationConfused classification

Yellowstone, 16 May 2007Yellowstone, 16 May 2007– Nearly same date as all previous scenesNearly same date as all previous scenes– Same band combinationSame band combination– Higher latitude and elevation = winter Higher latitude and elevation = winter

scenescene Worthless for interpretation!Worthless for interpretation!

– (Gorgeous though it may be)(Gorgeous though it may be)

15 May 20075,4,3

15 May 20077,5,2

Confused classificationConfused classification Northern Virginia, 15 May 2007Northern Virginia, 15 May 2007 Different bands can tell different storiesDifferent bands can tell different stories

– Recommendation: create classifications with all Recommendation: create classifications with all bands, except thermal (and pan on L7).bands, except thermal (and pan on L7).

All green things will be confused with each All green things will be confused with each other in 5,4,3. 7,5,2 gives you much more other in 5,4,3. 7,5,2 gives you much more distinction.distinction.

7,5,2 makes bright things too bright. 5,4,3 7,5,2 makes bright things too bright. 5,4,3 gives better distinction.gives better distinction.

Recommendation: Pick a different date for this Recommendation: Pick a different date for this area!area!– Too far into the growing seasonToo far into the growing season

Note: Mines: can be mixture of bare soil and Note: Mines: can be mixture of bare soil and waterwater– Regionally dependentRegionally dependent

Know what questions you’re askingKnow what questions you’re asking– Be clever about choosing imagesBe clever about choosing images– Know what types of land use or land Know what types of land use or land

cover you care aboutcover you care about Winter (leaf off): not usefulWinter (leaf off): not useful Early spring: target early greenupEarly spring: target early greenup

– Crop types & forest types (general)Crop types & forest types (general) Peak of greenPeak of green

– Max NDVI, clear cuts, barren landsMax NDVI, clear cuts, barren lands Late fall: target post-harvestLate fall: target post-harvest

– Crop fields from forestsCrop fields from forests

Geography MattersGeography Matters Changes between yearsChanges between years

– Similar seasonalitySimilar seasonalitySame dates don’t always work (take 2008)Same dates don’t always work (take 2008)

Know your geographyKnow your geography– Rules changeRules change

SeasonalitySeasonalityInterpretationInterpretation

– Land cover or land use typesLand cover or land use types– Scale of changeScale of change– Type of changeType of change

– Completely unknown study area is Completely unknown study area is doable, but difficultdoable, but difficult