1. 1. Relating NDVI to LAI across field, UAV and satellite data over orchards in a Mediterranean ecosystem Stephanie Debats Farid Faridani Marc Mayes Summer Course in Hydrology Universita Basilicata, Matera, Italy 27-31 July 2015
2. 2. Goals (and methods) Compare drone (pseudo) NDVI at different spatial scales (3m, 7m buffer) Compare across data types for tree crop canopies: Field data: LAI measured via light extinction w/LAI-2200 UAV: NDVI, high spatial resolution, DN values Landsat 8: classic NDVI, lower spatial resolution, calibrated to surface reflectance Evaluate performance of drone vs. satellite NDVI against past research
3. 3. Gamon et al. (1995), Ecological Applications PAST RESEARCH - NDVI vs. Field-Measured LAI (Leaf-Area Index) Relationships at satellite scales (Landsat 5) Question on the third point: How well does UAV data vs. satellite data of NDVI relate to LAI measured in the field?
4. 4. Study Area UAV flyover 29 July 2015 RGB: NIR G - B Landsat 8 28 July 2015 RGB: NIR [0.865 um] G [0.600um] B [0.485]
5. 5. Image Data & NDVI UAV NDVI = (NIR Blue)/(NIR+Blue) Landsat NDVI = (NIR Red)/(NIR + Red)
6. 6. Orchard crops: Kiwi supported on structure Peach Olive Young Apricots
7. 7. UAV NDVI Spatial Scale: 3m buffer
8. 8. UAV NDVI Spatial Scale: 7 m buffer
9. 9. Landsat NDVI and Field Measurements of LAI
10. 10. Comparison of Landsat and UAV NDVI
11. 11. Gamon et al. (1995), Ecological Applications SO: How well does UAV data vs. satellite data of NDVI relate to LAI measured in the field? How well does UAV pseudo-LAI perform?
12. 12. Kiwi Peach Apricot y = -0.0256x2 + 0.2368x + 0.2469 R = 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 1 2 3 4 5 6 NDVI-FieldAreaAverage LAI Field Measurement Landsat NDVI [field avg] vs. LAI [point avgs] PAST RESEARCH - Comparison to Field-Scale NDVI
13. 13. Kiwi Peach Apricot y = -0.0256x2 + 0.2368x + 0.2469 R = 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 1 2 3 4 5 6 NDVI-FieldAreaAverage LAI Field Measurement Landsat NDVI [field avg] vs. LAI [point avgs] PAST RESEARCH - Comparison to Field-Scale NDVI **NDVI averaged across three fields of variable LAI matches, very coarsely, past well- validated studies of NDVI-LAI relationships
14. 14. Note the axes. UAV estimated NDVI are ~15% >50% lower than LANDSAT-estimated NDVI. Many possible factors contribute: Camera data is in DN and uncalibrated to surface reflectance values, whereas Landsat is calibrated to surface reflectance Offset in camera NIR compared to actual NIR Lower spectral contrast/variability in pseudo-NIR Blue in camera than NIR Red in Landsat
15. 15. Summary Spatial scale (3m, 7m buffers) in UAV data show little difference in pseudo-NDVI Compare across data types for tree crop canopies: Reasonable contrasts and patterns observed between high-LAI, high-NDVI crops (kiwi), mid-LAI, mid-NDVI crops (peach, olive) and low-LAI, low-NDVI crops (young apricots) At field scale generalization, Landsat 8-NDVI coarsely matches past research on NDVI-LAI relationships Need more fields to validate this, as Landsat is coarse at the spatial scale of fields in Matera UAV NDVI is 15%-50%+ lower than Landsat 8-calculated NDVI Some refinements in UAV-NDVI needed to improve calibration to reflectance data needed to calculate NDVI properly. UAV data captures the same patterns in LAI-NDVI as Landsat despite difference in absolute values of NDVI