326 
Figure 2. Positions of test sites. 
the World Reference System was chosen as being repre 
sentative of the intensively cultivated Highveld 
region which produces a major portion of the country's 
grain products and also contains a variety of soils 
and crops (see Fig. 1). Nine test sites were selected 
to include the different soil types and crop produc 
tion patterns. The locations of the test sites are 
given in Fig. 2. Each test site contained ca. 100 
fields and was ca. 11 km x 7 km in size, representing 
about 50% cultivation. 
The area has a summer rainfall of 600 - 700 mm per 
year, has an altitude between 1400 and 1700 m above 
sea level and is fairly flat. The test sites have a 
maximum slope of 5% with a mean slope of 3%; thus no 
topographic problems were encountered. 
2.2 Ground reference data 
To facilitate the collection of ground reference data, 
the data set was divided into planting data and growth 
data. The planting data consisted of soil colour, 
planting date, crop type, cultivar, row spacing, row 
direction and seed density. These data were recorded 
for a sample of the 100 fields within each of the nine 
test sites. The growth stages of seven typical crops 
were defined by the Department of Agriculture (Malan 
and Turner, 1982). Codes of growth stage, average 
height, foliage distance, physical condition, weeds, 
disease and insect damage were monitored for some 
fields every 18 days coincident with the satellite 
overpass. The sample of fields comprised 48 maize, 5 
sorghum, 4 sunflower, 14 wheat, 1 potato and 1 oats. 
Data derived from 1:250 000 scale land type series 
of maps as published by the Soils and Irrigation In 
stitute of the Department of Agriculture and the sur 
face soil colour are tabulated in Table 1. The abbre 
viations used are defined on the land cover type maps. 
2.3 Satellite data 
Multispectral scanner (MSS) data sets were collected 
for 10 August 1979, 1 February 1980, 19 February 1980, 
13 April 1980, 19 May 1980 and 24 June 1980. These 
data sets were recorded on LANDSAT 3 and distributed 
in band-sequential format by EROS Data Center, USA. 
Eighteen data sets for the period November 1980 to 
December 1981 were recorded on LANDSAT 2 satellite and 
collected locally at the Satellite Remote Sensing 
Centre (SRSC) of the Council for Scientific and In 
dustrial Research (CSIR) in CCRS format (as used by 
the Canada Center for Remote Sensing). 
Table 1. Land characteristics. 
Test 
area 
Pedosystem 
Abbre 
viation 
Colour of surface 
soil 
BL 
Petrus Steyn 
Ca 
Grey with yellow 
DO 
Koppies 
Dc 
Dark brown to black 
DU 
Petrus Steyn 
Ca 
Brown to yellow-brown 
Blackhill 
Ea 
Black to brown-black 
ED 
Mooibult 
Bd 
Red-brown to brown 
Koppies 
Dc 
Dark brown to black 
GR 
Clifton 
Bd 
Red-brown to brown 
Blackhill 
Ea 
Black to black-brown 
LI 
Senekal 
Ca 
Brown to yellow-brown 
Koppies 
Dc 
Dark brown to black 
RE 
Petrus Steyn 
Ca 
Brown to yellow-brown 
VA 
Blackhill 
Ea 
Black to brown-black 
Koppies 
(Schultzdale) 
Dc 
Dark brown to black 
BR 
Petrus Steyn 
Ca 
Brown to yellow-brown 
3 DEVELOPMENT OF THE METHOD AND DATA ANALYSIS 
The steps taken to develop the method and to analyse 
the data were as follows: 
• The ground reference data were reformatted 
• field samples were located 
• the satellite data were standardized 
• suitable vegetation indices were defined 
• a Tasseled cap matrix was derived 
• field sample means were extracted from satellite 
data. 
Details are given below. 
3.1 Ground reference data 
Planting dates for six crops within each test site 
were extracted from the survey data (see Table 2). 
Crop calendars were generated as a means of display 
ing the temporal variability of the growth stages for 
the crops for each field. 
Table 2. Planting Dates for WRS 182-79 in 1981 (in 
day number) 
Test site 
Maize 
Sunflower 
Sorghum 
Wheat 
Potatoes 
Beans 
Bloukop 
279-283 
168-253 
BRAR 
293-298 
146 
285 
Dover 
328-358 
356-2 
342-345 
CXjndas 
295-310 
5 
144-202 
Edenville 
338 
336-342 
329-339 
76 
Grootvlei 
295-319 
3 
Reitz 
307-318 
329 
Overall 
range 
279-358 
336-5 
329-345 
141-253 
285 
329-3 
Planting 
period 
79 days 
34 days 
16 days 
112 days 
39 days 
3.2 The extraction of field sample data 
The field boundaries within each test site at 
1:50 000 scale were digitized and stored in raster 
image format. A mask within the monitored field 
boundaries was generated. All MSS data sets were