
Remote Sens. 2009, 1
975
Table 1. Dates, locations, sensors, residue and soil water contents, and comparisons of the
Cellulose Absorption Index (CAI), the Shortwave Infrared Normalized Difference Residue
Index (SINDRI), the Lignin-Cellulose Absorption Index (LCA), and the Normalized
Difference Tillage Index (NDTI). N, RMSE, and r
2
denote number of samples, root mean
square error, and coefficient of determination, respectively, in comparison between
spectral index value and line-point transect ground-truth of crop residue cover. Three-class
accuracy assessments (3 × 3 acc.) for 0%–15%, 15%–30%, and 30%–60% residue cover
classes for the four indices evaluated in this paper. Classification accuracy is assessed
using k-hat, an estimate of the kappa statistic, and the Z-statistic (Z-stat), which is used to
test the null hypothesis that classification accuracy is not significantly different from
chance. Comp. denotes composite (mean) values. Non-ASTER data were acquired using
either a ground-based spectroradiometer or an airborne hyperspectral sensor. CMD and
PIL denote Centreville, MD and Pesotum, IL, respectively. bna and dna denote “bands not
available” and “data not available”, respectively.
Location
Beltsville, MD CMD Ames, IA Fulton, IN PIL
Composite (mean) value
Date
20 May
2002
22 May
2002
10 Jun
2003
1 Jun
2004
2 Jun
2004
10 Apr
2007
22 May
2005
19 May
2007
27 May
2007
29 May
2006
6 Jun
2007
8 Jun
2006
Sensor
Ground
Air-
borne
ASTER
Air-
borne
Airborne
Air-
borne
N
77 95 41 41 71 32 107 104 104 95 136 37
Residue Water
g g
–1
0.09 0.08 1.80 1.10 0.10 dna dna dna dna dna dna dna
Soil Water
g g
–1
dna 0.09 0.30 0.28 0.09 dna dna dna dna dna dna dna
CAI
r
2
0.899 0.882 0.935 0.554 0.815 0.885 bna bna 0.821 0.798 0.829 0.722
0.814
RMSE
0.097 0.094 0.085 0.151 0.152 0.100 bna bna 0.078 0.117 0.107 0.128
0.111
3×3 acc.
0.829 0.779 0.902 0.732 0.761 0.813 bna bna 0.654 0.674 0.695 0.757
0.759
k-hat
0.68 0.63 0.84 0.13 0.61 0.66 bna bna 0.42 0.51 0.45 0.51
0.54
Z-stat
8.90 9.62 11.82 0.77 8.19 5.81 bna bna 5.26 6.73 5.43 3.62
6.61
SINDRI
r
2
0.853 0.811 0.769 0.640 0.835 0.596 0.611 0.605 0.674 0.821 0.834 0.868
0.743
RMSE
0.117 0.119 0.159 0.135 0.144 0.187 0.106 0.116 0.106 0.093 0.106 0.088
0.123
3 × 3 acc.
0.855 0.768 0.805 0.780 0.887 0.750 0.710 0.587 0.712 0.653 0.811 0.784
0.758
k-hat
0.73 0.61 0.69 0.43 0.81 0.53 0.42 0.30 0.51 0.48 0.68 0.57
0.56
Z-stat
9.93 9.19 7.48 3.22 12.96 4.13 5.56 3.95 6.93 6.39 10.16 4.21
7.01
LCA
r
2
0.815 0.767 0.634 0.487 0.842 0.651 0.575 0.632 0.664 0.390 0.618 0.860
0.661
RMSE
0.131 0.132 0.200 0.161 0.140 0.174 0.111 0.112 0.107 0.171 0.161 0.091
0.141
3 × 3 acc.
0.737 0.737 0.780 0.707 0.789 0.813 0.673 0.606 0.587 0.547 0.611 0.703
0.691
k-hat
0.51 0.55 0.64 0.09 0.63 0.66 0.34 0.33 0.29 0.34 0.34 0.43
0.43
Z-stat
6.18 7.87 6.61 0.57 7.71 5.51 4.04 4.11 3.67 4.17 4.22 2.97
4.80
NDTI
r
2
0.281 0.247 0.089 0.272 0.569 0.229 0.490* 0.640* 0.004 0.419 0.182 0.161
0.299
RMSE
0.258 0.227 0.316 0.192 0.232 0.259 0.122* 0.111* 0.185 0.167 0.235 0.222
0.210
3 × 3 acc.
0.618 0.589 0.366 0.780 0.634 0.563 0.720* 0.625* 0.462 0.463 0.589 0.649
0.588
k-hat
0.16 0.28 0.11 0.32 0.37 0.12 0.44* 0.37* 0.01 0.22 0.24 0.33
0.25
Z-stat
1.49 3.48 0.73 1.92 4.07 0.76 5.28* 4.94* 0.06 2.61 2.48 1.80
2.47
* denotes NDTI calculated by averaging ASTER Bands 5-8 into an equivalent Landsat TM band 7.
The second index, LCA [12], is a similarly devised index for the ASTER sensor:
LCA = 100·[2 ASTER6 – (ASTER5 + ASTER8)] (2)