The PGR technology was developed based on information derived from the NOAA AVHRR sensor.  The Advanced Very High Resolution Radiometer (AVHRR) provides four- to six-band multispectral data from the NOAA polar-orbiting satellite series. There has been fairly continuous global coverage since June 1979, with morning and afternoon acquisitions available. The resolution is 1.1 kilometre.

In 2003 the resolution for PGR will be improved to 250m (6.25Ha) by introducing the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor.  MODIS was launched on the Terra satellite in December 1999 and is designed  to observe and monitor the surface of the Earth. A second MODIS sensor was launched on the Aqua satellite in May 2002.  

The MODIS instrument has a wide spectral range, provides a significant improvement in spatial resolution (250m) compared to NOAA, and offers near daily global coverage.  MODIS will be used to generate weekly image composites. That is out of the 14 images we will get per week, we should be able to find some images where farms are not covered by clouds.  This should ensure any farm gets an updated PGR every week. 

Instruments on board both satellites measure the reflectance of both visible and invisible light from the earth’s surface, including vegetation such as pastures. The satellite imagery is converted into a Normalized Difference Vegetation Index (NDVI), a measure of the greenness of the pastures. This is then combined with climate information supplied by the Bureau of Meteorology to give estimates of PGR. 

We believe our PGR technology is unique because we provide quantitative estimates of PGR as kg/ha/day, rather than just a relative index of ‘greenness’ which is of little value for on-farm decision making.


In  2003 four possible satellites will be used to obtain satellite data for FOO estimations.  

LandSat TM-7  and LandSat-TM-5 (from July 2003 onwards) pass over every 16days with an 8 day lag between satellites and will provide high resolution images at with pixel size of 25 x 25 m.  

SPOT Satellites passes over every 3 to 5 days allowing improved control over the acquisition swath and also provides 25 x 25m pixels.  

The final alternative is to generate a Virtual TM image. The estimation of virtual FOO requires a Landsat TM-7 image from a previous pass to provide a starting FOO in combination with some clever mathematics using the predicted PGR from MODIS data over the period since the image was acquired.  Although there will be a reduction in resolution by combining a TM pixel with a MODIS pixel at 250 x 250 m,  it will help us fill the gaps when the other satellites have been unable to provide an estimate of FOO for that month.

Instruments on board all satellites measure the reflectance of both visible and invisible light from the earth's surface, including vegetation such as pastures.  As for PGR, the satellite imagery is converted into NDVI, and in turn used to give an estimate of feed-on-offer. 

Since 2001 teams of field technicians have collected thousands of ground measurements of pasture growth rate and biomass with which to validate the predicted values of FOO and PGR.


Copyright © 2003 Pastures from Space
Last modified: October 01, 2003

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