Water is Australia's most precious natural resource. The quality, quantity and
availability of this resource is the single factor most limiting agricultural development and
sustainability in this country.
Since the development of Australia's cotton industry in the 1960's, and the expanding
areas of irrigated crop, there has been an increasing demand placed on the limited water
resources of the country. Consequently, the cotton industry has been the target of protest from
conservation groups, residents of rural townships and others farmers engaged in competing
rural sectors. Therefore, cotton farmers need to develop best practice in terms of water use
efficiency. Not only does this make good ecological sense but also good economic sense.
Traditional methods of irrigation scheduling have proven to be subjective and haphazard.
Recently developed methods, while providing more quantitative techniques, do not give a
synoptic view of a field's or region's crop moisture status.
The main objective of this project was to evaluate an airborne thermal scanner (8-12 µm) as practical tool for monitoring the water requirements of an irrigated cotton crop. The
thermal scanner was mounted below a light aircraft and imagery was collected over Field 86 ,
Togo Station, north-west NSW during the summer of 1990/91. The field was divided into
nine treatments for the purpose of this project. Three irrigation regimes (early, normal and
late) with three repetitions were applied to the nine treatments.
A total of fourteen images were selected for analysis. These images were grouped into
sets of AM images, PM images as well as diurnal groupings which were interpreted for three
separate dates during the growing season. Ground based measurements of infrared crop
surface and soil temperature, soil moisture deficit, leaf area index (LAI) and the Crop Water
Stress Index (CWSI) were collected to calibrate the airborne imagery.
Imagery was in the first instance visually interpreted to determine what information
could be gained from this technique. Patterns on the imagery were related to diurnal
variations in soil and crop temperatures. This investigation revealed a number of soil related
phenomena inherent to the field which were influencing the airborne detected temperatures.
While this technique showed variability across the field, the interpretation was somewhat
subjective.
Temperature values were extracted from the imagery in order to conduct an analysis
of variance (ANOVA) between the airborne and ground measurements of infrared crop
surface temperature. In summary, this analysis did not show a strong relationship between the
airborne and ground based measurements. A number of contributing factors have been
proposed as the reason for this variation in the two datasets. Pearson's correlation analysis
was applied to the AM (r = 0.65) and PM (r = 0.32) groups of airborne and ground
temperatures.
Airborne derived calculations of the CWSI were compared to ground based
measurements for the AM group of flights. These derived values were only acceptable in
instances where the ANOVA results had shown them to approximate the ground based
measurements.
While airborne thermal imagery provides a useful tool for determining general
variations in temperatures across a field, there are many additional factors, the most dominant
being the thermal characteristics of the background soil, which influence the detected
temperatures. This technique does not provide the precise quantitative information required
to accurately determine across-field measurement of the CWSI.
| Identifer | oai:union.ndltd.org:ADTP/219176 |
| Date | January 1996 |
| Creators | Malouf, Christopher P., n/a |
| Publisher | University of Canberra. Resource, Environmental & Heritage Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Christopher P. Malouf |
Page generated in 0.002 seconds