T. Tokola et al., POINT ACCURACY OF A NONPARAMETRIC METHOD IN ESTIMATION OF FOREST CHARACTERISTICS WITH DIFFERENT SATELLITE MATERIALS, International journal of remote sensing, 17(12), 1996, pp. 2333-2351
The reference sample plot (RSP) method is a distance-weighted k neares
t neighbour estimation method, which allows simultaneous interpretatio
n of several variables. In the RSP method, the k spectrally nearest fi
eld plots are looked at separately for each unknown pixel, and the are
a weight of the unknown pixel is divided as a function of the spectral
distances to the nearest plots. The RSP method was examined in a fore
st inventory for estimating stem volumes by tree species groups using
different satellite materials. Two methods were tested both in searchi
ng for and weighting the nearest field plots. Euclidean distance funct
ions worked steadily with all the volume variables studied. The other
distance measure tested was based on regression modelling. With more t
han 15 plots, both covariance weighting and inverse distance weighting
gave similar results. Considering the held data of this study, the su
itable number of the nearest plots in plotwise estimation appeared to
be between 10 and 15 plots. With Landsat TM, SPOT XS and SPOT P, the d
ifferences in standard errors were minor. When combined TM and SPOT P
were used, the plotwise standard error of total volume was still over
60 per cent.