RETRIEVING BRDF OF DESERT USING TIME SERIES OF MODIS IMAGERY

1. IGRSS 2011, Vancouver , Canda RETRIEVING BRDF OF DESERT USING TIME SERIES OF MODIS IMAGERY Haixia Huang, Bo Zhong, Qinhuo Liu, and Lin Sun Presented by Bo Zhong bzhong1@gmail.com Institute of Remote Sensing Applications, Chinese Academy of Sciences

2. Outline • Background • Methodology • Preliminary results • Applicatoins • Conclusions

3. 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

4. Problem • There is no “good” BRDF product of desert

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

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

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

9. AOD retrieval using DO method

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

11. 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, 11-20, 21-30, 31-40, and 41-50); • Using Staylor-Suttles BRDF model instead of Walthall BRDF.

12. Preliminary results MODIS-B3: Staylor-Suttlescoefficients

13. MODIS-B1: Staylor-Suttlescoefficients

14. MODIS-B2: Staylor-Suttlescoefficients

15. Comparison with MODIS products

16. R2 much higher • RMSE is lower

17. 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

18. Spectral matching

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

21. The chosen desert sites

22. The geolocations of the deserts

23. Taklimakan desert

24. Rabal-Khali desert

25. Lybia desert

26. Saharadesert

27. 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

28. Thank you for your attention!