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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
In this work, various crop and environmental variables of the
coffee crop were evaluated, as well as the spectral response of
coffee fields, surveyed and georefferenced on the field, using
TM/Landsat 7 images in bands 3, 4 and 5 and the SPRING
software from INPE. The objective of the work was to establish
the correlation between the selected variables and their spectral
responses, in order to obtain identification patterns of the coffee
crop in Landsat images.
2. METHODOLOGY
Two 520 km” study areas were selected, around the city of
Patrocinio, representative of the physiographic region of Alto
Paranaiba, and around the city of Machado, representative of
the physiographic region of Sul de Minas. These areas represent
two of the state's most important regions in coffee production.
They are located in different environments, with different
production systems, the Sul de Minas with traditional
management practices and long historical information and the
Alto Paranaiba with modern and entrepreneurial farming. This
information is registered by the respective local associations and
was important to the development of this work. The two pilot-
areas were selected from previous investigations on areas that
best represented the production regions of Alto Paranaiba
(Patrocinio) and Sul de Minas (Machado). The Alto Paranaiba is
characterized by flat plateaus with altitudes varying from 820 to
1100 m, favorable climate, subject to low-intensity frosts,
moderate water deficiency, flat, gently undulating to undulating
slopes, predominance of Latosols, possibility of producing fine
beverages and high technology production systems. In the
region of Sul de Minas, areas with altitudes varying from 780 to
1260 m, favorable climate, subject to frost, moderate water
deficiency, gently to steep slopes, predominance of Latosols and
soils with argillic B horizons, possibility of producing fine
beverages, medium to high technology production systems. The
pilot-area of Machado was delimited by the coordinates UTM
278 Km and 304 Km W and 7.942 Km and 7.922 Km S,
encompassing portions of Patos de Minas and Monte Carmelo
topographic maps of the Brazilian Army, at the scale of
1:100.000. The pilot-area of Machado was delimited by the
coordinates UTM 392 Km and 418 Km W and 7.620 Km and
7.600 Km S, encompassing portions of the topographic maps of
IBGE (Brazilian Geographic Institute), scale 1:50.000, sheets of
Machado and Campestre.
TM/Landsat 5 digital images used were image orbits 220/73
(Patrocínio) and 219/75 (Machado), bands 3, 4 and 5, from
April-June/1999, the period of coffee's greatest vigour and
when the field surveys were carried out. Band 3 (red - 0,63 to
0,69 pm) is sensitive to green, dense and uniform vegetation. It
presents great absorption, turning dark and allowing a good
contrast between the areas occupied by vegetation and those
unoccupied (exposed soil, roads and urban areas). It also
presents good contrast between different types of vegetation
(grazing fields, savanna and forest) and permits drainage
mapping through visualization of the gallery forest along the
rivers’ courses in regions with little vegetation cover. Band 4
(near-infrared - 0,76 to 0,90 um) allows the dense, green and
uniform vegetation to reflect a lot of energy and to appear in a
very light shade, and is thus recommended for studies of
spectral responses of areas occupied by green vegetation. This
band presents good contrast between soil and water, allowing
the mapping of large rivers, lakes, reservoirs and humid areas,
as well as morphology of the terrain, burned vegetation,
geology and geomorphology and aquatic vegetation. Band 4 is
also very sensitive to the absorption of electromagnetic
171
radiation by iron and titanium oxides, very common in tropical
highly weathered soils. Band 5 (mid-infrared - 1,55 to 1,75 pum),
allows the observation of humidity levels in the plants and the
detection of possible stress due to lack of water. Band 5 is also
used to obtain information on soil humidity. However, it may
suffer perturbations if rain occurs just before the satellite images
the area.
The choice of study area was very important in the development
of the work and its results. A few characteristics of the area,
desirable or not, taken into account in the study were: plantation
systems; cropping practices, coffee cultivars representative of
those existent today in Brazil; age, slope gradient and aspect
variability and size of the fields compatible to the resolution of
the TM sensor (not less than 1 ha); easy access; extension
sufficient to obtain an adequate number of samples.
In all, 75 coffee fields were surveyed and georeferenced with
the GPS Garmin 12. In Machado, due to the great variation of
relief, of planting and cropping systems and the smaller size of
the coffee fields, samples were collected in various farms to
better represent the region. In Patrocinio, due to the more
homogeneous conditions of the relief and the plantations,
samples were collected in only one farm, which presented all
the variables important to the characterization of the region,
encompassing a total of 1000 ha, distributed in its 22 different
fields.
The variables observed in the field surveys, carried out during
the period of the coffee’s greatest vigour (April to June), were:
area of the field, age, height or plant size, average diameter of
the plants, year of pruning, percentage of the terrain occupied
by coffee plants, type and percentage of ground cover by plant
canopy in the row, cultivars, plant density, spacing between
plants and rows, vegetative vigour, average production, slope
gradient, slope aspect and soil type.
Among these variables, a few were selected for statistical
analysis, as listed below:
l. Size (SIZE): average height of coffee plants
in a field in meters;
Plant Density (DENS): number of plants
per hectare;
3. Vegetative vigour (VIG): evaluation of the
coffee plants vegetative state, carried out in
the field, by ranking each coffee field with
marks varying from 1, for minimum vigour
to 10 for maximum vigour;
4. Diameter (DIAM): average diameter of
plants in a coffee field in meters;
5. Production (PROD): average plant coffee
production in liters of coffee berries per
plant;
6. Ground cover (COV): percentage of the
ground covered by plants canopies in a
coffee field. Calculated according to the
average diameter and the spacing used;
7. Slope gradient (SLO): percentage of slope
gradient of a coffee field.
D
The data was organized in electronic spreadsheets and inserted
in digital databases created for each pilot-area with the aid of
the geographic information system SPRING. The images were
treated with the SPRING Images module, followed by
registration, atmospheric correction and correction of the solar
elevation angle to obtain the reflectance values of the sampled
