# Presentation: 196470

## Surface Reflectance (SR) Validation

**Milestones:**  	Beta SR product available, regionally, by March 31, 2004
- 			*[Provisional SR suite, NAM, by March 31, 2005]*
- 			Validated SR suite, NAM, by March 31, 2006
**Validation should cover the following areas of concern:**
- 	- Cirrus contamination
- 		- quantify the effect of mistaking cirrus for aerosol
- 		- can we use MODIS to get around this problem for ETM+?
- 	- Heterogeneous landscapes (semi arid, agriculture, etc) and adjacency effects
- 		- may need separate dark target thresholds for different biomes
- 		- atmospheric correction enhancements include adjacency effect correction
- 	- Variable topography
- 		- topographic illumination correction can come later

## Four Technical Approaches for SR Validation:

- Comparison of Landsat SR with MODIS MOD09A daily SR swath product (ETM+ only)
- 	- compares ETM+ SR values (aggregated to 500m) and MODIS values obtained within 1⁄2 hour of each other
- 	- some concern about BRDF – MODIS is “nadir corrected SR”, Landsat product is not
- Comparison of Landsat dark-target aerosol retrievals with AERONET Aerosol Optical Thickness (AOT) data (TM and ETM+)
- 3.     Comparison of Landsat SR with airborne SR retrievals (MSS, TM, ETM+)
- 	- examples include Barnes MMR, SE590, ASD flown for field campaigns, with sun photometer data collected at same time
- 	- difficult to find exactly simultaneous Landsat imagery – must make due with imagery collected +/- 10 days.
- 	- need to be careful of radiometer calibration, flight conditions, bandpass, etc.
- Visual inspection of multiple Landsat scenes corrected to SR
- 	- anticipate that atmospheric correction should reduce scene-to-scene variability if imagery gathered within 16-32 days.
- 	- residual scene boundaries tell us about problems in atmospheric correction.

## Validation Site Selection Criteria

- Is there field data (radiometer, AOT) available for comparison to Landsat?
- Is someone already working on this area (e.g. LTER sites?)
- Do we include a diverse suite of land conditions?
- Do we sample a diverse suite of atmospheric conditions?
- Can this site be used later for forest change mapping and validation?

## Proposed Validation Sites and Data Availability

**BOREAS (18 path-rows Northern Canada)**
-  Landsat data: Geocover triplet + 1994 imagery
-  2000-2002 MODIS SR comparisons
-  1994 MMR observations
-  **FIFE (1 PR Kansas, 1989 imagery)**
-  Landsat data: 1989 imagery
-  1989 AOT measurements
-  1989 helicopter MMR observations
-  1989 TM corrected SR images using in-situ AOT
-  **Cascades (~6 PRs Pacific NW, Geocover + 1989-90 OTTER + AeroNET)**
-  Landsat data: Geocover triplet + 1989-1990 imagery
- 1989-90 SE-590 OTTER ultralight observations
-  1994-2002 HJ Andrews Aeronet data
-  2000-2002 MODIS comparisons
-  **Mid-Atlantic (~9 PRs, Geocover + AeroNET)**
-  Landsat data: Geocover triplet + 1994-2002 imagery
- 2000-2002 MODIS comparisons
-  1994-2002 Wallops, GSFC Aeronet data
**SNF (1 PR Michigan, 1982-83 imagery)**
-  1982-83 helicopter MMR observations
-  Comparison with 1982-83 MSS data
-  **Jornada (1 PR New Mexico, 2000-2001 imagery)**
-  2001-01 MQUALS airborne data

## Field radiometer comparison site

- Large-area validation area

- Forests (from UMD landcover)

- AERONET comparison site

## Space

- 2000 Geocover (ETM+)

- 1990 Geocover (TM)

- 1975 Geocover (MSS)

- Aeronet Comparisons

- Field Campaign
- Radiometer Comparisons

- Time

- One Landsat path-row

- Schematic diagram showing the space-time image distribution for a SR validation site.  Large multi-scene comparisons utilize the Geocover archive.  Repeated acquisitions of individual path-rows for Aeronet comparisons and comparisons with field radiometer data