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Product pages » Normalized Difference Vegetation Index (NDVI) - AVHRR, without atmospheric correction, Australia coverage

Normalized Difference Vegetation Index (NDVI) - AVHRR, without atmospheric correction, Australia coverage

Last modified by Matt Paget on 2016/06/29 05:11

Normalized Difference Vegetation Index (NDVI) - AVHRR, without atmospheric correction, Australia coverage

ndvi200908.png

Figure 1: Monthly NDVI for August 2009.

Link to the data

DescriptorData link
Persistent URLhttp://www.auscover.org.au/purl/avhrr-ndvi-bom
GeoNetwork recordhttp://data.auscover.org.au/geonetwork?uuid=3745d0ae-7e0f-4985-ba83-e647349616c2
NetCDF-CFhttp://opendap.bom.gov.au:8080/thredds/catalog/avhrr_ndvi__1km_one_third_month/catalog.html
http://opendap.bom.gov.au:8080/thredds/catalog/avhrr_ndvi_1km_monthly/catalog.html
http://opendap.bom.gov.au:8080/thredds/catalog/avhrr_ndvi_5km_monthly/catalog.html

Data licence and Access rights

ItemDetail
RightsCopyright for any data supplied by the Bureau of Meteorology is held in the Commonwealth of Australia and the purchaser shall give acknowledgement of the source in reference to the data. Apart from dealings under the Copyright Act 1968, the purchaser shall not reproduce (electronically or otherwise), modify or supply (by sale or otherwise) these data without written permission from the supplier.
LicenceBureau of Meteorology data licence.
AccessThese data can be freely downloaded and used subject to the Rights statement. Any use of this data should include acknowledgement of the satellites of NOAA as the original source of the satellite data, and acknowledgement of the Commonwealth of Australia (Bureau of Meteorology) which received and processed the data into ndvi, and acknowledgement of the CSIRO which developed the code to process the NOAA satellite data, and the AusCover Project which funded the creation of this file (http://data.auscover.org.au/citation). We ask that you send us citations and copies of publications arising from work that use these data.

The Rights and Access statements copy those which is present in the version 1 NetCDF-CF files. The licence will be updated to CC BY for future releases.

Alternate Title

AVHRR Normalised Difference Vegetation Index 1-Month Australia 0.05degree GEO Grid v20100421

Abstract or Summary

The Normalised Difference Vegetation Index (NDVI) data are derived from satellite data. The data provides an overview of the status and dynamics of vegetation across Australia, providing a measure of the amount of live green vegetation. The satellite data comes from the Advanced Very High Resolution Radiometer (AVHRR) instruments on board the National Oceanic and Atmospheric Administration (NOAA) series of satellites that are operated by the US (http://noaasis.noaa.gov/NOAASIS/ml/avhrr.html).

Monthly NDVI is a composite of the NDVI values from cloud-free observations in the month from the operational afternoon NOAA satellite. There are, in the absence of cloud, usually one and sometimes two observations per day. The satellite data are processed initially onto a 0.01x0.01 degree grid and then averaged to a 0.05x0.05 degree grid. The data is available within a few days after the end of a month.

The AVHRR data from April 1992 to June 2008 were generated by CSIRO (http://www.eoc.csiro.au/cats). Data from July 2008 onward were received and processed by the Bureau of Meteorology. For key processing steps, CSIRO and the Bureau both use the Common AVHRR Processing System (CAPS) software developed by CSIRO. CAPS Modular Processing applies geolocation, calibration, cloud masking, sea masking and regridding. Calibration drift detrended and normalised to NOAA-14 by invariant semi-arid IBRA regions. No atmospheric or angular corrections are applied. Compositing is by maximum value NDVI.

Spatial and Temporal extents

ItemDetail
Spatial resolution (degrees)0.01° (1 km) and 0.05° (5 km)
Spatial coverage (degrees)110 to 155 E, -10 to -45 N
Temporal resolution10 day and 1 month
Temporal coverage1992-04 to ongoing
Sensor & platformAVHRR
ItemDetail
Spatial representation typegrid
Spatial reference systemWGS 84

Point of contact

ItemDetail
NameDr Ian Grant
OrganisationBureau of Meteorology
PositionResearch Scientist
Emaili.grant@bom.gov.au
Roleauthor
Address
Telephone
URLhttp://www.bom.gov.au

Keywords

ThesauriKeyword
GCMDEARTH SCIENCE > BIOSPHERE > VEGETATION > VEGETATION INDEX
CFnormalized_difference_vegetation_index
FoREnvironmental Sciences > Ecological Applications = 0501

There are three main thesauri that AusCover recommends:

  1. Global Change Master Directory (http://gcmd.nasa.gov)
  2. Climate and Forecast (CF) convention standard names (http://cfconventions.org/standard-names.html).
  3. Fields of Research codes (http://www.abs.gov.au/ausstats/abs@.nsf/0/6BB427AB9696C225CA2574180004463E?opendocument).

Data quality

While the AVHRR instruments are calibrated before launch, their calibration changes in orbit, typically with a rapid change immediately after launch and then drifting during their mission lifetime of several years. Furthermore, the AVHRR carries no on-board calibration system for the reflective channels. Therefore, consistency of calibration over the length of the NDVI time series was achieved by adopting the procedure developed for use in Australia by the Environmental Resources Information Network (ERIN). This procedure adopts the calibration published by Rao and Chen of NOAA in 1999 using a stable Libyan desert site for the NOAA-14 segment of the time series, and then assumes the reflectance stability of a set of Australian arid sites to detrend the calibration of the other satellites and match them to NOAA-14. The use of the arid-site detrending technique to establish the long-term calibration consistency implies that while the temporal stability of these NDVI data is expected to be comparable to the best available to date for AVHRR NDVI time series covering Australia, the data cannot be relied upon to make absolute statements about long-term trends.

While the US NOAA satellite program aims for continuous quality coverage of the afternoon orbit, contingencies in the operation of the spacecraft and in the processing requirements have introduced periods of no coverage or reduced data quality. Specifically:

  • Data commences in April 1992, and is contiguous, except for a gap from October 1994 to January 1995 due to the lack of a sensor following the unexpected end of NOAA-11 operation.
  • Coverage and quality are reduced during the winters of 1993, 1994 and 2000 due to very low sun elevations (and consequent shadowing on the surface) during the last year or so of operation of some satellites.
  • Data for September 2003, and possibly October, November and December 2003, display some artefacts due to a NOAA-16 sensor scan-motor problem.

Validation status

No validation information is available for AVHRR NDVI. The AVHRR surface reflectances from which the NDVI is calculated could be validated against:

  • Higher quality surface reflectances derived from other satellites, in conjunction with the improved processing leading up to the dataset update.
  • Top-of-canopy reflectances measured by AusCover validation activities.

References

ItemDetail or link
Publicationhttp://www.bom.gov.au/climate/austmaps/about-ndvi-maps.shtml
Report to BRSNDVI_anomalies_BoM_for_BRS_procedure (Word, 44kb)
Validation report
BoM grid data and mapshttp://www.bom.gov.au/jsp/awap/ndvi/index.jsp
Tutorialhttp://earthobservatory.nasa.gov/Features/MeasuringVegetation

Algorithm summary

The NDVI anomalies are produced from data from the AVHRR instrument carried by the series of polar orbiting satellites operated by the US NOAA. The NOAA-11, -14, -16 and -18 satellites are used, which are all in afternoon orbits. The AVHRR images each location in Australia in daytime at least once daily, in five or six spectral bands. Bands 1 and 2 make the measurements of red and near-infrared reflected sunlight, respectively, from which NDVI is calculated, while other bands measure the Earths thermal emission.

For key processing steps, CSIRO and the Bureau both use the Common AVHRR Processing System (CAPS) software developed by CSIRO. CAPS Modular Processing applies geolocation, calibration, cloud masking, sea masking and regridding. No atmospheric or angular corrections are applied.

The cloud mask applied by CAPS is a modification of the CLAVR-1 scheme developed by NOAA, and uses the reflective and thermal bands. The data are regridded using nearest neighbour interpolation to a 0.01-degree geographic grid spanning the Australian continent. NDVI is calculated from the red and near-infrared (band 1 and band 2) reflectances as NDVI = (rNIR - rRed) / (rNIR + rRed).

A single satellite orbit over Australia is typically received at more than one ground station, as two to four swaths with substantial overlap. These are merged into a single file: by CSIRO as data in a low-level format ("stitching") before CAPS processing; and by the Bureau of Meteorology as regridded data after CAPS processing.

Orbits are composited into three periods in each calendar month - the 1st-10th, 11th-20th and 21st-end of the month - by the NDVI Maximum Value Composite (MVC) method. Besides greatly reducing data volumes, compositing improves spatial completeness and temporal consistency at individual locations. After rejecting pixels with solar zenith angle exceeding 80°, these three sub-monthly composites are further composited by maximum NDVI value to produce the one-month composites on a 0.01x0.01 degree grid. These are averaged to a 0.05x0.05 degree grid, excluding sea pixels.

Product version history

Version labelDetail
1.0Initial release

A new version of these datasets, with processing that includes explicit corrections for atmospheric and angular effects, will begin processing in 2012/Q3.

Metadata history

DateDetail
2011-06-29Metadata creation date
2013-02-16Reformatted to new template.
Consolidated metadata between inconsistent wiki and geonetwork records.
Copied licence information from NetCDF-CF files. Will want to update this to CC BY for the next version.
Tags:
Created by Matt Paget on 2013/02/16 18:58

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