# Presentation: 743482

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Crystal Schaaf
- Center for Remote Sensing
- Boston University

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- NPP/NPOESS EDR calls for a (cloud-free) shortwave albedo with the atmospheric state at time of overpass
- Broadband instantaneous albedos only – no spectral albedos
- The NGST VIIRS land albedo algorithm has been delivered utilizing two retrieval approaches:
- Dark Pixel Surface Albedo (DPSA) based on MODIS heritage
- Bright Pixel Surface Albedo (BPSA) based on a direct-estimate top-of-atmosphere method

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Heritage MODIS implementation provides periodic BRDF and Albedo retrievals over land.
- A BRDF is retrieved for each pixel where sufficiently high quality and well distributed cloud-free observations are available to characterize the surface anisotropy
- Albedos (integrals of the BRDF) are intrinsic surface quantities and are governed by the surface cover, vegetation state, and structure

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Current MODIS product uses both Terra and Aqua  to obtain periodic retrievals of BRDF
- At 500m every 8 days (based on a 16-day window)
-  Daily albedos are produced by coupling these periodic BRDFs with instantaneous observations
- BRDF provides *a priori* description of the surface character
- Instantaneous observation provides measure of surface and atmospheric state.
- Note: BRDFs are also used by the community to correct directional observations to a common view geometery
- Nadir BRDF-Adjusted Reflectance (NBAR)

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Long term NPP Land Science Team concerns
- Broadband instantaneous albedo is not sufficient
- Most modelers are interested in spectral albedos
- No access to underlying spectral BRDF IP
- NGST implemented two algorithms (DPSA and BPSA) for land with no guidance on relative quality
- Original scheme: BPSA for pure snow and DPSA elsewhere
- Ocean Albedo algorithm implemented but Sea Ice not addressed

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Recent Disappointing Developments
- Still no access to spectral albedos and BRDF IP
- Specifications relaxed
- albedo produced at 1km but evaluated at 4km
- Sea Ice albedo only within 0.3
- Sea Ice Albedo algorithm implemented
- direct-estimate top-of-atmosphere method
- BPSA has been declared primary algorithm over all surfaces

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- MODIS Product Evaluation and Validation
- V005 reprocessed product
- 500m tiled, every 8 days (16 day window)
- 30arc sec, 0.05degree global climate model grids (CMG)
- Gap filled BRDF (continuation of the collaboration with the Atmospheres Team)
- 30arc sec, 0.05degree CMGs
- 500m tiled (in collaboration with the NACP effort)
- Validation of the MODIS BRDFs with POLDER
- Extensive Validation over the ARM Southern Great Plains site
- CLASIC field campaign
- tower albedometers, Cloud Absorption Radiometer (CAR)
- Scale tower/CAR/MODIS with high res imagery/land cover
- ARCTAS field campaign

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Gap-filled Global BRDF Product

**5-year composite maps of the MODIS BRDF (Isotropic Parameter, P0) at Band1 using **_**high quality**_** full inversions only (Left) before gap-filling and (Right) after gap-filling in January (Top) and July (Bottom). Histogram stretch: 0-388.**

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Validation with POLDER-3/PARASOL
- Selection of sites for a variety of land covers Nov 2005-Oct 2006.

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- Validation with POLDER-3/PARASOL
- Selection of sites for a variety of land covers Nov 2005-Oct 2006.

## MODIS and VIIRSAlbedo and Reflectance Anisotropy (BRDF)

- CLASIC field campaign over the ARM Southern Great Plains site
- Tower data
- CAR

**  ****250-500m****	****	****          1km****	****	****  0.05degree**

**J-31 CAR Flight Track Map**