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- 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. 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. 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. 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. Image Data & NDVI UAV NDVI = (NIR Blue)/(NIR+Blue)
Landsat NDVI = (NIR Red)/(NIR + Red)
- 6. Orchard crops: Kiwi supported on structure Peach Olive Young
Apricots
- 7. UAV NDVI Spatial Scale: 3m buffer
- 8. UAV NDVI Spatial Scale: 7 m buffer
- 9. Landsat NDVI and Field Measurements of LAI
- 10. Comparison of Landsat and UAV NDVI
- 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. 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. 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. 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. 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