Data Summary
Title: NDVI ( Normalised Difference Vegetation Index ) - High resolution gridded monthly NDVI dataset ( 1992 onwards )
Status: onGoing
Start Time: 1971-01-01
End Time: now
Geographical Extent (deg):
West: 112.85
East: 155.39
South: -45.9
North: -9.2
Data Details
Abstract
Monthly and multi-monthly (1,3,and 6 month periods) high resolution vapour pressure grids, for 1992 onwards.
The grids show the vapour pressure values across Australia, in the form of two-dimensional array data.
These grids are re derived from satellite data.
The data provides an overview of the status and dynamics of vegetation across Australia, providing a measure 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 ).
Supplementary Information:
Arc/InfoTM grids - all Australia
MONTHLY grid data files are available, 1992 onwards, for 'NDVI Average', and 'NDVI Anomoly'.
Grid map images are available, per 1,3 and 6 month period, from 1992 onwards.
Anomalies are calculated with respect to the 1992 to 2008 reference period.
For an explanation of the above variables, see : http://www.bom.gov.au/climate/austmaps/about-ndvi-maps.shtml
Purpose:
Live green vegetation absorbs visible light (solar radiation) as part of photosynthesis. At the same time plants scatter (reflect) solar energy in the near infrared. This difference in absorption is quite unique to live vegetation and provides a measure of the greenness of the vegetation. NDVI is an index which measures this difference, providing a measure of vegetation density and condition. It is influenced by the fractional cover of the ground by vegetation, the vegetation density and the vegetation greenness. It indicates the photosynthetic capacity of the land surface cover.
Keywords:
(Type: theme)
- climate analyses
- Vegetation Index ( NDVI ) - average for a given month - gridded
- Vegetation Index ( NDVI ) - anomoly for a given month - gridded
Keywords:
(Type: theme)
- DataType: Gridded
- DownloadableData
Citation Details
Title: NDVI ( Normalised Difference Vegetation Index ) - High resolution gridded monthly NDVI dataset ( 1992 onwards )
Resource Date:
2014-01-14T00:14:00
(creation)
Identifier:
Code: http://www.bom.gov.au/metadata/19115/ANZCW0503900404
Identifier Authority Title: ANZLIC Identifiers
Identifier Authority Date:
2008-10-29
Party To Be Cited:
Organisation: Australian Bureau of Meteorology
Role: originator
Point Of Contact For Dataset
Point Of Contact: Australian Bureau of Meteorology
Web: Bureau of Meteorology
website: feedback form [http://www.bom.gov.au/other/feedback]
(WWW:LINK-1.0-http--link)
, Function: information
Custodian: NCC Information Officer, Australian Bureau of Meteorology
Owner: Australian Bureau of Meteorology
Data Extent
Extent Description: Australia
Geographical Extent (deg):
West Bound Longitude: 112.85
East Bound Longitude: 155.39
South Bound Latitude: -45.9
North Bound Latitude: -9.2
Temporal Extent:
Start Time: 1971-01-01
End Time: now
Description: 1971 to now
Dataset Constraints
Dataset Legal Constraints:
Access Constraints: copyright; otherRestrictions
Use Constraints: copyright; otherRestrictions
Other Constraints:
Please note that the copyright 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. Please contact us (see details below) for more information.
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Data Information
Data Distribution Information
Monthly high resolution NDVI grids - LATEST month- webpage [http://www.bom.gov.au/jsp/awap/ndvi/index.jsp]
(WWW:LINK-1.0-http--link)
, Function: search
Monthly high resolution NDVI Average : all months (1992 onwards) ARCHIVE webpage [http://www.bom.gov.au/jsp/awap/ndvi/archive.jsp?colour=colour&map=ndviave&period=month&area=nat]
(WWW:LINK-1.0-http--link)
, Function: information
DownloadableData : Monthly high resolution NDVI average : grid data file : Latest month [http://www.bom.gov.au/web03/ncc/www/awap/ndvi/ndviave/month/grid/latest.grid.Z]
(WWW:LINK-1.0-http-link)
, Function: download
DownloadableData : Monthly high resolution NDVI anomoly : grid data file : Latest month [http://www.bom.gov.au/web03/ncc/www/awap/ndvi/ndvianomsd/month/grid/latest.grid.Z]
(WWW:LINK-1.0-http--link)
, Function: download
Monthly high resolution NDVI Anomoly : all months (1992 onwards) ARCHIVE webpage [http://www.bom.gov.au/jsp/awap/ndvi/archive.jsp?colour=colour&map=ndvianomsd&period=month&area=nat]
(WWW:DOWNLOAD-1.0-ftp--download)
Monthly high resolution NDVI Average : latest 6 months : webpage [http://www.bom.gov.au/jsp/awap/ndvi/index.jsp?colour=colour&time=latest&step=0&map=ndviave&period=6month&area=nat]
(WWW:DOWNLOAD-1.0-ftp--download)
Monthly high resolution NDVI Average : latest 3 months : webpage [http://www.bom.gov.au/jsp/awap/ndvi/index.jsp?colour=colour&time=latest&step=0&map=ndviave&period=3month&area=nat]
(WWW:DOWNLOAD-1.0-ftp--download)
Point of truth URL of this metadata record [http://www.bom.gov.au/metadata/19115/ANZCW0503900404]
(www link)
, Function: information
Data Quality
Scope:
Level: dataset
Lineage:
Statement: 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 national map shown on the web is based on the 0.05x0.05 degree grid, sub-sampled at every fifth point to give an effective resolution of 0.25x0.25 degrees. The regional maps are based directly on the 0.05x0.05 degree grids, so there may be some slight differences in the fine detail between the national map and the regional maps.
All grids and maps may be updated from time to time as the processing algorithms are improved with, for instance, better satellite calibration or cloud masking. A date stamp at the bottom right-hand corner of each map indicates when the analysis was produced.
Multiple-monthly NDVI
The 3-month and 6-month grids are averages of the one-month grids. They are generated monthly and are available within a few days after the last month of the averaging period.
NDVI standardised anomaly
The NDVI standardised anomaly is the departure of NDVI from the long-period average, normalised by the long-period variability. It indicates whether the vegetation greenness at a particular location is typical for a particular compositing or averaging period of the year, or whether the vegetation is more or less green.
Monthly anomalies are generated from the monthly NDVI dataset by subtracting the long-period mean and dividing by the long-period standard deviation for that month of the year, for each grid cell. The reference period is 1992 to 2008, excluding the poor quality months of April to September 1994 (due to low sun elevations, resulting in excessive shadowing on the ground) and September 2003 (due to satellite instrument scan anomalies).
For the 3-month and 6-month anomalies the NDVI values are averaged over the three or six months in question, and normalised by the mean and standard deviation calculated over all instances of those months over the reference period except for the poor quality months listed above.
Analysis technique
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.
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. No atmospheric or angular corrections are applied.
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 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. The data from January 2006 to June 2008 comes from Alice Springs receiving station only.
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.
Map Projections
The map projections used are either Cylindrical Equidistant (CE) or Lambert Conformal (LC). The Lambert Conformal projection takes three parameters; the central longitude (in degrees east of the Greenwich Meridian) and two standard parallels of latitude (in degrees south of the equator). For more details, see: http://www.bom.gov.au/climate/austmaps/about-ndvi-maps.shtml
Reference System
Code: GDA 94
Code Space: Geocentric Datum of Australia
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Metadata Information
Metadata Identifier: ANZCW0503900404
Hierarchy Level: dataset