RETRIEVING BRDF OF DESERT USING TIME SERIES OF MODIS IMAGERY Haixia Huang, Bo Zhong, Qinhuo Liu, and Lin Sun Presented by Bo Zhong Institute of Remote Sensing Applications, Chinese Academy of Sciences IGRSS 2011, Vancouver, Canda

Outline  Background  Methodology  Preliminary results  Applicatoins  Conclusions

Background  BRDF is the key parameter for: Quantitative remote sensing Erath radiation budget More  Desert is one of the main landcover types Strongly reflecting the solar radiation More

Problem There is no “good” BRDF product of desert

Methodology-flowchart MODIS imagery Converting DN to TOA reflectance Identifying the “ clearest ” of each observations Retrieving reflectance of “ clearest ” observations Fitting to Staylor-Suttles BRDF model Lookup Tables BRDF of desert

Methodology- site choosing Location of the experimental site (MODIS imagery color composite) Cole view of the site (TM imagery color composite)

Methodology- site choosing  It is stable, so it can be seen as an invariant object;  There are a lot of lakes within the calibration site, which are seldom polluted, so the lowest AOD of calibration site can be determined by Dark Object (DO) method using Landsat TM and ETM+ data.

8 （ a ） Mar. 3, 2000 （ b ） Feb. 3, 2010 Methodology- site choosing

AOD retrieval using DO method ETM+ imaging date Aerosol optical depth TM imaging date Aerosol optical depth

Original method Time series of MODIS imagery Identifying clear pixels Reflectance of clear pixels BRDF fitting Reflectance of hazy pixels AOD of hazy pixels LUT MODIS surface reflectance

Modifications for the original method  AOD determination for the “clearest” days;  Shrinking the use of the algorithm from globe to the desert calibration site, which is stable;  Identifying the “clearest” observations for every 10 degrees in view zenith angles from 0-50 degree (0-10, , 21-30, 31-40, and 41-50);  Using Staylor-Suttles BRDF model instead of Walthall BRDF.

MODIS-B3: Staylor-Suttles coefficients Preliminary results

MODIS-B1: Staylor-Suttles coefficients

MODIS-B2: Staylor-Suttles coefficients

Comparison with MODIS products

R 2 much higher RMSE is lower

Applications I: inter-calibration of AVHRR using retrieve BRDF  Spectral matching of AVHRR and MODIS  AVHRR data simulation using the new method  Inter-calibration  Validation

Spectral matching AVHRR 1 (0.645 μm) AVHRR 2 (0.865 μm) AVHRR 3 (1.6 μm) aiai

Applications II: global desert BRDF retrieval  Mapping of the desert  BRDF and AOD retrieval simultaneously using the new method  Preliminary validation

The chosen desert sites

The geolocations of the deserts Desert Name Lat （ ° ） Lon （ ° ） Altitude （ m ） Duration (yyyy.mm.d) Taklimakan39.0°N-40°N84°E-85°E Rabal- Khali 18.8°N-19.8°N45.5°E-46.5°E Lybia24°N-25°N12°E-13°E Sahara19.5°N-20.5°N8°W-9°W

Taklimakan desert

Rabal-Khali desert

Lybia desert

Sahara desert

Conclusions  The new method is able to catch the BRDF characterization of deserts  This method can be used for inter-calibration of reflective bands of moderate satellite data like AVHRR  This method is helpful for researches on earth radiation budget

Thank you for your attention!