# Presentation: 420674

## A surface reflectance standard product from LDCM and supporting activities 

**Principal Investigator**
**Dr. Eric Vermote **
**Geography Dept., **
**University of Maryland**
**Co. P.I. **
**Dr. Chris Justice **
**Geography Dept., **
**University of Maryland**

## Message from the PI 

- MONDAY

## Rationale for the research activities

- The Surface Reflectance standard product developed for MODIS provides the basis for a number of higher order land products for global change and applications research
- A similar approach could work for LDCM
- It is possible to implement an operational robust, globally applicable and fully automated correction as part of the LDCM processing chain, with the code made openly available for others to use (e.g. LDCM ground stations).
- The algorithm has already been tested by the NASA LEDAPS project (an operational protoiype).

##  Atmospheric effect has a strong impact on remotely sensed data

**MODIS Granule over South Africa  (Sept,13,2001, 8:45 to 8:50 GMT)**

- RGB no correction
- for aerosol effect

- RGB surface reflectance (corrected for aerosol)

- Corresponding aerosol optical thickness  at 670nm (0 black, 1.0 and above red) linear rainbow scale. Clouds are in magenta, water bodies are outlined in white.

## BOREAS ETM+ scene

**BOREAS ETM+ scene**
- Scene: p033r021
- Date: 09/17/2001

**Top-of-atmosphere TOA                                 Surface Reflectance **

## Approach for the surface reflectance product 

**Atmospheric correction consistent with the MODIS and NPP VIIRS approach, ensuring consistent reflectance data across resolutions based on rigorous radiative transfer **
- _[http://6s.ltdri.org](http://6s.ltdri.org/)_
- _[http://](http://rtcodes.ltdri.org/)__[rtcodes.ltdri.org](http://rtcodes.ltdri.org/)__[/](http://rtcodes.ltdri.org/)_

## Validation and uncertainty estimates. Theoretical error budget developed, comprehensive evaluation.

**Validation and uncertainty estimates. Theoretical error budget developed, comprehensive evaluation.**

- FOREST

- SAVANNA

- SEMI-ARID

- Error ~0.5% in reflectance units

## AERONET-An Internationally Federated Network

- Characterization of aerosol optical properties
- Validation of Satellite Aerosol Retrievals
- Near real-time acquisition; long term measurements
- Homepage access http://aeronet.gsfc.nasa.gov:8080/

## Approach for the surface reflectance product -  2003 AERONET results 

- about 5000 cases analyzed

## 2000-2007 Results (25,542 cases)88.85% of band1 data were within the error bars (+/- 0.005 +0.05 ro) 

- Version 2 AERONET (i.e. with background correction and spheroid)

## Toward a quantitative assessment of performances (APU)

- 1.3 Million 1 km pixels
- were analyzed for each
- band.
**Red** =  Accuracy (mean bias)
**Green** = Precision (repeatability)
**Blue** = Uncertainty (square sum of
- A and P)
**On average well below magenta **
**theoretical error bar**

## Landsat cloud/cloud shadow mask

- Use the surface reflectance / thermal band (based on MODIS experience)
- 1) First step cloud and snow mask (visible and thermal) undertaken prior to aerosol inversion
- 2) Second step - aerosol is derived and surface reflectance product is generated
- 3) On the corrected data for non-snow pixels, clouds are derived from Red-Blue anomaly (Red-Blue/2 >0.03) (Whiteness) for land pixels (1.6mic >0.05 – water test), additional test (Blue >0.30 and Temperature < NCEP based Threshold) is performed to account for saturation in the blue.
- 4) Clear pixel temperature (thermal band) used to compute reference air temperature used in estimate of cloud height, for the shadow mask algorithm, which is based on a hybrid geometric and spectral approach

## Example of Landsat cloud/cloud shadow mask

## Simple Cloud Mask Clouds are in yellow

## Expanded Detail

**Yellow, Orange**: clouds
**Blue**: Adjacent to cloud
**Dark Green**: Shadow
**Light green**: Clear

## Comparison with ACCA 

- First version of simple cloud algorithm run on 2500 scenes (122 scenes, ACCA validation data set)
- Initial result shows good consistency w. ACCA showing slightly more cloud
- Identifying those scenes with large differences for further evaluation
- Will also compare Landsat scene stats with MODIS cloud stats
- General Issue – how do you evaluate cloud mask accuracy ?

## Next Steps on theAtmospheric Correction Work 

- Further Evaluation of Landsat SR product
- Continued comparison with MODIS
- Develop APU for L7
- Evaluate early prototype OLI SR processing at EDC?
- Initial version of SR code delivered to EDC
- Project to develop LDCM ‘operational’ version, to be tested initially with L7
- Continued Refinement
- Attention to coastal regions / water
- Evaluate use of MODIS aerosol models for Landsat
- Evaluate need for Adjacency Effect correction
- Determine need for solar zenith angle correction /BRDF effects
- Further Evaluation of Simple Cloud Mask
- Extend the comparison with ACCA and MODIS
- Common test scenes with AT ACCA
- More work on testing shadow mask

## Recommendations 

- Thermal capability on LDCM would certainly enhance the cloud detection with OLI data
- Will need to address pixel/geometry co-location of data from two instruments
- LDCM should provide a Surface Reflectance product
- early testing of ‘operational’ code/production suggested w. proxy data
- Greater ST participation desired in evaluation of OLI instrument testing and performance results (e.g. w. attention to band to band registration, cross-talk, saturation levels, SNR etc)
- Protected web access to data and results as needed  / periodic telecons / an updated Testing Schedule
- Instrument performance through product evaluation SR, NDVI TOC, Cloud Mask (using proxy data)
- Next ST Meeting 1 Day for Topical Working Groups
- Suggest a cloud/shadow focus group (try to develop consensus approach for standard processing)

## Update on Related Developments  

- GEOSS Ag 0703  Global Agricultural Monitoring Task
- New secretariat at ISRO (Ahmedabad)
- Requirement for 3-5 day repeat, mid-res’n, cloud free coverage during growing season (this should influence NLIP planning beyond another Landsat)
- Data policy workshop planned for China, Spring 08 (USGS participation will be needed)
- GOFC/GOLD and START African Regional Network Data Initiative (NASA-GOFC funding)
- Build on the resent USGS Landsat web-enabled data initiative
- Regional network nodes to provide data to regional scientists without internet
- EDC requested to host visiting scientists –  extraction extract data, take back data on disc, some capacity building on data management
- Letter of request for participation sent to USGS and UNEP Grid
- Upcoming NASA LCLUC ST Meetings
- Thailand (w. MAIRS/APN on Tropical Land Use Systems), January 09
- Washington, March ’09 – climate and land use
- Data issues to be addressed - GLS 2005 and 2010, 1995? and Products
- SAXTA (NASA funded Landsat P2P)
- Project completed - system developed and tested
- System available to USGS as needed