Airborne Imaging Spectrometer (AIS) data were acquired over an agricultural area in eastern San Joaquin County, California in July, 1984. Cover type information was subsequently collected for all fields along this flight line. The lack of detailed ground data on individual fields, however, limited AIS data analysis to a qualitative comparison of the spectral reflectance curves for a total of nine cover types. Based on this analysis, it appears that cover types with a positive slope in the 1550 to 1700 nm region have a higher spectral response in the 1200 to 1300 nm region compared to those cover types with a negative slope in the 1550 to 1700 nm region. Within cover type, spectral variability was also found to be greater than that between cover types. Given the lack of additional field data, the reason for these differences is a matter of speculation

Wood, B. L.

Wrigley, R. C.

English

NASA Technical Reports Server

AIS INVESTIGATION OF AGRICULTURAL MONOCULTURES N86-11640 
BYRON L. WOOD, Technicolor Government Services, Inc., 
NASA/Ames Research Center, Moffett Field, CA, USA; ROBERT 
C. WRIGLEY, NASA/Ames Research Center, Moffett Field, CA, 
USA. 
ABSTRACT 
Airborne Imaging Spectrometer (AIS) data were acquired 
over an agricultural area in eastern San Joaquin County, 
California in July, 1984. Cover-type information was 
subsequently collected for all fields along this flight 
line. The lack of detailed ground data on individual 
fields, however, limited AIS data analysis to a qualitative 
comparison of the spectral reflectance curves for a total of 
nine cover types. Based on this analysis, it appears that 
cover types with a positive slope in the 1550-1700 nm region 
have a higher spectral response in the 1200-1300 nm region 
compared to those cover types with a negative slope in the 
1550-1700 nm region. Within cover type, spectral variability 
was also found to be greater than that between cover types. 
Given the lack ,of additional field data, the reason for 
these differences is a matter of speculation. 
INTRODUCTION 
For several years, the NASA/Ames Research Center 
(NASA/ARC) has been involved in the application of remote 
sensing data to agricultural research in California. During 
the 1983 growing season, researchers at NASA/ARC and the 
University of California, Berkeley -cooperated in the 
collection of ground data including: crop type, growth 
stage, percent ground cover, canopy height, surface 
moisture, weediness, row direction/width and irrigation 
method on over 200 fields in eastern San Joaquin County, 
California. The collection of these data was coordinated 
with the acquisition of Daedalus Thematic Mapper Simulator 
(TMS) data on seven dates throughout the growing season. 
These data were used both to evaluate Landsat Thematic 
Mapper (TM) resolution data for crop identification and 
mapping and to understand the relationship between changes 
in surface/crop conditions and spectral reflectivity. 
One of the findings of this research was that at the 
level of TM data resolution, considerable spectral crop 
confusion results from the relationship between crop canopy 
structure, percent ground cover and soil moi sture content. 
In an effort to address this issue, Airborne Imaging 
Spectrometer data were requested for a portion of the San 
Joaquin County study area. The intent was to coordinate the 
collection of ground data with the acquisition of the AIS 
134 
https://ntrs.nasa.gov/search.jsp?R=19860002173 2020-03-23T06:29:51+00:00Z
data. Ground data collection was to include those variables 
monitored in 1983, as well as plant tissue for laboratory 
spectral and chemical analysis. In actuality, it proved 
impossible to coordinate these activities and only cover 
type information was obtained several weeks after the AIS 
flight. 
DATA ACQUISITION AND ANALYSIS 
The AIS, mounted on the NASA C-130 aircraft, acquired 
data along Jack Tone Road in eastern San Joaquin County, 
California on July 31, 1984. These data cover the 
wavelengths between 1155 and 2336 nanometers (nm) at a 
sampling interval of approximately 9.3 nm. Ground 
resolution of the data is approximately ten meters with a 32 
pixel swath width. 
The 35-mm black and white photographs, acquired at the 
same time as the AIS data, were used to locate the flight 
line, and served as the base on which field cover-type data 
were recorded. The field reconnaissance took place in late 
August, 1984. Due to this delay, some of the fields 
identified as bare soil may have supported a crop at the 
time of the AIS overflight. Whenever possible, these fields 
were labeled as to previous cover type. If there was any 
question about cover type at the time of the AIS overflight, 
the field was not included in the subsequent analysis. 
Analysis of the AIS data was performed on a VAX 11/780 
using IDIMS image processing software and additional 
programs developed specifically for AIS analysis. All AIS 
channels were registered for analysis purposes. No other 
preprocessing (i.e., atmospheric correction) was, however, 
attempted. 
For each of the nine cover types identified along Jack 
Tone Road, one or more two-by-two pixel areas were extracted 
and labeled. The spectral values ~or all 128 channels were 
then plotted. A preliminary analysis of the different cover 
types was undertaken to determine the maximum reflectance 
value ~gainst which other cover types could be scaled. Of 
the nine cover types identified, stubble had the highest 
reflectance values and, therefore, became the reference 
cover. Other cover types included: corn, alfalfa, beans, 
sugar beets, tomatoes, peppers, vineyards, and bare soil. 
An adobe clay soil was found throughout the study area. 
DISCUSSION 
Since the only ground data available to this study was 
cover type, discussion of results is both preliminary and 
speculative. Other researchers may opt to interpret these 
data differently based on a greater knowledge of vegetation 
135 
" 
response in the 1165-2336 nm region. 
Figures 1 and 2, which show reflectance curves for 
beans and sugar beets, respectively, are typical of the 
general patterns observed for most other cover types. The 
positive slope in the 1550-1700 nm region for beans (.3) and 
sugar beets (.2) corresponds with higher reflectance values 
in the 1200-1300 nm region. The negative slope in the 
1550-1700 nm region observed in beans (.1) and sugar beets 
(.1) corresponds with lower reflectance values in the 
1200-1300 nm region. 
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Figure 1. AIS spectra for two bean samples. The positive 
slope in the 1550-1700 nm region is associated with a higher 
response in the 1200-1300 nm region. The negative slope in 
the 1550-1700 nm region is associated with a lower response 
in the 1200-1300 nm reg ion. Unlike sugar bef3ts, beans are 
cultivated during a definite season and, as such, all fields 
should be about the same age. The difference in slope is, 
therefore, not easily explained on the basis of growth stage 
or age alone. 
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WAVELENGTH (NM) 
Figure 2. AIS spectra for two sugar beet samples. The 
positive and negative slopes of the reflectance curves in 
the 1550-1700 nm region are clearly evident as was the case 
for beans (Figure 1). Since sugar beets are cultivated 
year-round, it is nearly impossible to determine the growth 
stage for the individual fields. 
The negative slopes for beans (.1) and sugar beets (.1) 
are similar to the curves shown in Figure 3. All bare soil 
plots exhibited this same general shape. The similarity 
between these curves suggests that either the soil 
background is influencing the reflectance (lower percent 
ground cover), field conditions are drier, or the plants are 
undergoing senescence. 
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WAVELENGTH (NM) 
Figure 3. AIS spectra for alfalfa, beans, peppers, 
tomatoes, and stubble. All these crops have a negative 
slope in the 1550-1700 nm region. Although the shape of the 
reflectance -curves are similar, the values are different. 
If not for the similarity of the curves in Figure 4, it 
would seem likely that the difference was simply a matter of 
crop-type differences. 
Since no ground data were available for well-watered 
fields, with complete canopy cover, it is difficult to 
substantiate the idea that the positive slope in the 
1550-1700 nm region corresponds to such conditions. This 
view is supported, however, in part, by the higher 
reflectance in the 1200-1300 nm region which is 
characteristic of healthy active-growing crops. Figure 4 
shows four fields which follow this general pattern. All 
have positive slopes in the 1550-1700 nm region and 
relatively high and consistent values in the 1200-1300 nm 
region. Not only are the shapes of these curves similar, 
138 
but the reflectance values along them are fairly similar. 
This is surpr1s1ng, given the considerable. differences 
between the four crops in terms of size, canopy shape, and 
growth char.acteristics. 
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Figure 4. AIS spectra of alfalfa, corn, beans, and sugar 
beets. All these crops are examples of the positive slope 
in the 1550-1700 nm region. Although the reflectance curves 
are' similar, the crops are different in terms of structure, 
canopy, and growth characteristics. 
The negative phase in the 1550-1700 nm region is shown 
for five cover types in Figure 3. Although the curves are 
similar in terms of overall shape, they exhibit considerable 
variability in reflectance values. Given the similarity of 
the curves in Figure 4, this difference in reflectivity can 
not be explained solely on the basis of different cover 
type. It may, ~owever, be a function of changes in the 
plant as it becomes subject to moisture stress or reaches 
maturity. In either event, reflectivity should change 
139 
throughout the spectrum. 
other leaf components will 
reflectivity. 
CONCLUSIONS 
As moisture content decreases, 
have a greater influence on 
Based on a preliminary, qualitative analysis of AIS 
data acquired over an agricultural area in eastern San 
Joaquin County, some basic differences between crop spectral 
profiles have been identified in the 1155-2336 nm region. A 
positive slope in the 1550-1700 nm region corresponds with 
higher reflectance values in the 1200-1300 nm region. This 
does not appear to be related to crop type. A negative 
slope in the 1550-1700 nm region corresponds with lower 
reflectance values in the 1200-1300 nm region. This also 
does not appear to be related to crop type. 
The positive and neg~tive slopes in the 1550-1700 nm 
region seem to be related to plant moisture content, or 
differences in leaf chemistry growth stage. All crops with 
the positive slope had similar reflectance curves, 
regardless of considerable differences in crop structure and 
growth characteristics. This suggests that whatever factor 
is the dominant influence on reflectance in the 1155-1336 nm 
region is common to all of the crops studied. 
Crops with a negative slope in the 1550-1700 nm region, 
although exhibiting similar overall reflectance curves, show 
considerable differences in terms of absolute reflectance 
values. These differences may be a result of changes in 
plant structure, moisture content, mineral uptake and, 
hence, leaf chemistry as th'e plant matures and approaches 
senescence. 
In order to answer the questions raised by these 
spectral curves, one needs to collect considerable and 
detailed field and laboratory data regarding profiles of the 
plants of interest over time. Agricultural environments are 
excellent areas in which to undertake these studies since 
conditions are uniform over a broad region where they can be 
easily measured, and since the entire sequence of plant 
development stages occur in a relatively short period of 
time. 
140 ! ~ 


AIS Investigation of Agricultural Monocultures

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