Introduction

Our approach to remote sensing involves the use of video cameras - one infra-red and one coloured - housed in an aerodynamically designed aluminium capsule which is strapped to the strut of a high winged aircraft, e.g. a Cessna 172. Cables from the aluminium pod are tied to the strut of the aircraft and run down through the bottom of the door into the back seat where two video recorders and associated equipment are situated. The aircraft has two viewers - one for the pilot and one for the video operator. In conjunction, a global positioning system is used for coordination of the specified target, e.g. crops, woodlands or areas affected by salinity. The tapes are then returned to base and can be either viewed through a VCR or individual frames can be selected, captured by computer and still prints produced. Through our local farm discussion group in Donald- Farm Vision 2000 - we had the opportunity to visit Neville Sharpe's farm at Two Wells in South Australia in September 1992. Here we witnessed Neville's first attempt at videoing crops from an aircraft. From those early beginnings Neville, with the aid of Iain Grierson from the Coopertive Research Centre in Adelaide, has now developed the project to the stage where we consider it to be suited to our needs. By this we mean it must be:

(a) affordable

(b) user friendly

(c) versatile

The Equipment

Good quality equipment is essential for satisfactory results. We are using super VHS recorders for this reason, although for many purposes the normal VHS is adequate. Hi 8 recorders are of similar quality to super VHS and their compactness ideal, but they are prone to visible tape vibration because of the small tape, so would need to be insulated from the vibration of the plane if they are used. A wide angle lens is used with the cameras. At 2500 feet the camera takes in about a 600m wide strip, which is adequate for many paddocks. This also means that the plane can fly below the cloud layer so the system can be used on a higher proportion of days. Some distortion occurs particularly at the edges of the image, but this can be adjusted in the computer if necessary. Although smaller computers can handle an image, a 486 with 8 meg of ram is an appropriate computer. It must be fitted with a frame grabber card andshould have a photstyler type software program or a specifically designed program to enable maximum flexibility in enhancing the image.

Results

The value of having both colour and infrared is demonstrated in the examples.

1. Compaction. The extremely wet harvest of 1992 meant that trucks carting grain out of the paddock caused a great deal of compaction. This was picked up by the infrared camera 2 years later even though it is not visible on the colour film or to the naked eye.

2. Stubble burning. A small fire burnt a patch of wheat in 1992. This patch was still visible especially on the infrared in wheat in November 1994.

3. Aphids. Several poor patches of canola crop which were visible on both colour and infrared proved to be aphid infestation when inspected from the ground.

4. Fertility. Areas which missed out on urea stood out clearly on the infrared. Even where the differences were very obvious, such as where the spreader drove too wide, it was hard to see on the ground.

5. Salinity. The poor growth on salt affected areas can be clearly identified particularly on the infrared frame. Videoing the same area over a number of years will give a record of changes in the area affected by salting.

6. Soils. Different soil types are easily seen and mapped to help with management in the future.

The Future

The system is very versatile and easy to use so it just takes some imagination to work out its potential. Iain Grierson from CRC in Adelaide is testing a thermal camera to add to the system. Indications are that it will pick up a wider range of differences than the current system. Similarly, using filters to select a narrow range of light especially at the infrared end of the spectrum has the potential to identify specific plant species. Mapping shallow soils with low water holding capacity can be done by flying when the pasture on those areas starts to dry out but while the rest of the area is still growing. This can only help when deciding on the appropriate management of these areas.

Conclusion

To be useful, any system must be easy and cheap to use, and must be readily available when required. The system we are looking at fits these criteria. While there is less detail recorded than in other systems, it is perfectly adequate for assisting in management decisions on the farm.