CitationDelamater, Paul L.; Messina, Joseph P.; Qi, Jiaguo; & Cochrane, Mark A. (2012). A Hybrid Visual Estimation Method for the Collection of Ground Truth Fractional Coverage Data in a Humid Tropical Environment. International Journal of Applied Earth Observation and Geoinformation, 18, 504-514.
AbstractA substantial body of research exists exploring the spectral unmixing of remotely sensed image data. Specifically, we refer to the attempts and successes to model the percent vegetation cover (2-dimensional horizontal density) within a pixel, known as fractional coverage (fc). With this paper, we present a hybrid visual estimation method for fc field data collection in the complex landscapes found in humid tropical environments. The method includes a scalable theoretical model of fc, integrates the visual estimation technique with hemispherical photography collection, and is conducted over a systematic ground collection area. We present results from a case study conducted in the humid tropical region of Ecuador. Specifically, we report on the relationship between fc data modeled using a linear NDVI transformation and observed fc data collected using our hybrid visual estimation method. Our study found a significant, positive linear relationship (β=0.795, r2>0.84, and p<0.001) between modeled and observed fc values. Because the accuracy of both modeled and observed values are unknown, a full validation of the proposed method of collection is not possible. Therefore, we conduct an error assessment, identifying limitations in the modeling method (e.g., non-linear relationship between modeled and true values and potential for saturation) and hybrid ground-truth collection method (e.g., subjectivity of visual estimation and positional errors in the ground collection area) that explain the deviation from a 1:1 relationship. We believe the proposed method of ground truth data collection is a significant contribution towards efforts to validate biophysical information gained from remotely sensed data.
Reference TypeJournal Article
Journal TitleInternational Journal of Applied Earth Observation and Geoinformation
Author(s)Delamater, Paul L.
Messina, Joseph P.
Cochrane, Mark A.