1. An improved satellite-based long record of
Australian vegetation dynamics: AVHRR NDVI
Ian Grant and Paul Loto’aniu (Bureau of Meteorology, AusCover)
Rob Smart (ABARES)
Presentation by Ian Grant, Bureau of Meteorology

2. What is NDVI?
• Normalised Difference Vegetation Index
• Satellite index of vegetation greenness
• Change in red/near-infrared contrast
Blue Red Infrared

3. What is NDVI?
• NDVI is influenced by both
• Plant vigour and health
• Vegetation cover fraction
• NDVI indicates
• Biomass production

4. What is NDVI?
• Time series monitors seasonal vegetation dynamics
• Enables spatial and interannual comparisons
Arid
Agricultural

5. What is NDVI?
• NDVI anomaly assesses departure of vegetation
condition from long-term mean for the month
Standard deviations from 17-year mean

6. NDVI on AusCover
Bureau of Meteorology THREDDS server
• Monthly AVHRR NDVI
• 0.01° and 0.05°
• netCDF format

7. NDVI Applications
• Agricultural assessment
• Grazing land management
• Drought monitoring
• Hydrological modelling
• National Carbon Accounting System
• National Agricultural Monitoring System (NAMS)
• Assess Exceptional Circumstances drought assistance
• Water balance modelling

8. NDVI Applications
Hydrological modelling
• AVHRR NDVI converted to
leaf area index
• Time series tracks response
of forested catchment to
disturbance (bushfire,
clearing, …)

9. Why improve AVHRR data?
Long time series
• MODIS starts 2000 (to ~2015)
• AVHRR starts 1982 (to ~2020)
Improve
• Spatial and temporal consistency
• Consistency with MODIS
Not just NDVI
• Surface reflectance in two bands: Red & NIR
• NDVI = (NIR – Red) / (NIR + Red)
• Albedo ≈ (NIR + Red) / 2  Climate and water models
• Biophysical variables: fAPAR, LAI

10. Processing chain
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction (needs atmospheric parameters)
• Compositing OR Angular normalisation

11. Reception
DAR
TWN
ALS
PER
CPT
HOB

12. Processing chain
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction (needs atmospheric parameters)
• Compositing OR Angular normalisation

13. Stitching
Orbit stitching
• Reduce data volume
• Improve quality

14. Processing chain
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction (needs atmospheric parameters)
• Compositing OR Angular normalisation

15. Compositing
Merge data from several days to
Stitched orbits
• Complete spatial coverage
• Fill gaps due to cloud
• Reject residual cloud
Compositing
National coverage

16. Processing chain
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction (needs atmospheric parameters)
• Compositing OR Angular normalisation

17. Processing chain
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction (needs atmospheric parameters)
• Compositing OR Angular normalisation

18. Processing chain - The past
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration
• Cloud masking
• Atmospheric correction
• Compositing OR Angular normalisation

19. Processing chain – AusCover
Phase 1
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration (improved)
• Cloud masking
• Atmospheric correction
• Compositing OR Angular normalisation
First application of atmospheric correction to Australia’s
AVHRR stitched archive

20. Processing chain – AusCover
Phase 2
• Reception
• Collation and reformatting
• Stitching
• Georeferencing
• Calibration (improved)
• Cloud masking (improved)
• Atmospheric correction
• Compositing OR Angular normalisation

21. Calibration
Use NOAA cross-calibration results
• AVHRR vs MODIS
• AVHRR vs AVHRR
• Heidinger et al. 2010

22. Atmospheric correction
CSIRO scheme for atmospheric radiative transfer
•Mitchell and O’Brien (1993)
Total column water vapour Aerosol Optical Depth
• Numerical weather model • Chemical transport model
• European Reanalysis (ERA) • ECMWF/MACC
Interim • Validated against
• Validated against radiosondes sunphotometers

23. Atmospheric correction
Before After

24. Immediate applications
Immediate
• National Land Use map (ABARES)
• Hydrological modelling (BoM)
• National grassland curing and fire danger index history
Then?
• National evapotranspiration history
• National carbon flux history
• Also, reflectance and albedo