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Title
Remote sensing for resources development and environmental management
Author
Damen, M. C. J.

225
ation of the
•ibed by equa-
lation of the
the ratio of
ind of infra-
the soil at
l to one. The
ition in the
1 explicitly.
1 to be a more
ared reflec-
:e the actual
various spec-
method 1 com-
¡asurements in
rhich the green
) for calcu-
nce, whereas
1 reflectances
(1 and 2) may
tance cannot
the recording
s explicitly
Results for
le 2 and fi-
2 gave sim
arse results
is indicates
ail reflec-
!S. The con-
id by method 2
d 0 or 1 was
i of LAI is
asymptotic
:ance, and it
.g. from a
is an ex-
¥s in consid-
.ues, but with
LAI
Figure 3: Regression of LAI on corrected infrared
reflectance, using method 0. Field trial 116, vege
tative stage, 1982.
LAI
Figure 4: Regression of LAI on corrected infrared
reflectance, using method 1. Field trial 116, vege
tative stage, 1982.
LAI
the regres-
.ectance for
it measure-
esulting in
did not vary
: of the curve,
¡reals and in
leasurements
malysis of
er treatment
nteractions
ients (LAI),
1 out on re-
i spectral
itter vari-
;ly smaller
can be as-
;ans of con-
sis of vari-
¡timated LAI
results of
ile with the
riginal LAI
ime variable.
:or correcting
:ly estimating
efficient of
1 of
[duals
figure
.217
3
.230
4
.214
5
Figure 5: Regression of LAI on corrected infrared
reflectance, using method 2. Field trial 116, vege
tative stage, 1982.
Table 3 lists the means, estimated coefficients of
variation (CV) of residuals and the critical levels
in testing for treatment effects for the LAI (field
measurements) during the vegetative stage of the
crop, resulting from an analysis of variance. The
variance was determined by means of appropriate
averaging of inter-plot and intra-plot variances.
The CV is the ratio of the square root of the mean
squares of residuals and the mean value of the de
pendent variable. The critical level (often called
P-value) is the smallest level of significance at
which the observed result would just lead to rejec
tion of the null hypothesis (that a treatment has no
effects). On 19 May the interaction effect between
sowing date and nitrogen nutrition was significant
at the 5 % level (meaning that the effects of nitro
gen nutrition were dependent on the sowing date).
The nitrogen nutrition effect was significant on
17 June.
The results of the analysis of variance for the
infrared reflectance data obtained are listed in
table 4 (the infrared reflectance relates best to
LAI). On most dates, critical levels in testing for
treatment effects by means of infrared reflectance
measurements were smaller than those obtained by
means of LAI measurements, with the exception of a
large critical level for sowing date effect on
10 June. Thus treatment effects could be ascertain
ed with larger power with reflectance measurements
than with LAI determination in the field. This is
the main reason for preferring reflectance measure
ments over sampling in field trials. This conclu
sion is also confirmed by the magnitude of the co
efficients of variation. CV values in the infrared
band were considerably smaller than CV values for
LAI. However, one has to keep in mind that infra
red reflectance and LAI are different characteris
tics and therefore one should be careful when com
paring these results.
With the results of table 2 it is possible to
estimate the LAI per plot from the reflectance mea
surements (method 2) and subsequently to apply an
analysis of variance on these LAI estimates. The
results of such an analysis of variance are listed
in table 5. Results for 28 April 1982 are not list
ed, because bare soil predominated on that date.
Similarly to the results for the infrared reflec
tance, the critical levels in testing for treatment
effects in LAI estimates were smaller than those in
the LAI measurements (table 3) on most dates. Thus,
treatment effects on LAI could be ascertained with
larger power by reflectance measurements than by
taking samples in the field. This was confirmed by
Table 3: LAI: means, CVs and critical levels in
testing for treatment effects, obtained on conse
cutive sampling dates. Field trial 116 in 1982.
date
mean
CV
critical
interaction
level in
sowing
dates
testing:
nitrogen
nutrition
19
May
0.99
0.215
0.030
0.003
0.011
3
June
3.67
0.363
0.474
0.092
0.277
17
June
5.27
0.256
0.920
0.123
0.004
Table 4:
critical
obtained
in 1982.
Infrared reflectance (%): means, CVs and
levels in testing for treatment effects,
on consecutive missions. Field trial 116
date
mean
CV
critical
interaction
level in
sowing
dates
testing:
nitrogen
nutrition
28 April
13.8
0.056
0.587
0.012
0.885
17 May
15.4
0.021
0.003
0.001
0.001
27 May
33.6
0.034
0.000
0.001
0.000
10 June
47.9
0.071
0.864
0.465
0.001
17 June
53.0
0.033
0.565
0.013
0.000
Table 5: LAI estimated by reflectance measurements:
means, CVs and critical levels in testing for treat
ment effects, obtained on consecutive missions. Field
trial 116 in 1982.
date mean CV critical level in testing:
interaction sowing nitrogen
dates nutrition
17
May
0.48
0.099
0.000
0.002
0.000
27
May
2.42
0.075
0.000
0.001
0.000
10
June
4.47
0.152
0.906
0.814
0.002
17
June
5.70
0.073
0.279
0.110
0.000