Artificial Neural Network Modeling of High Arctic Phytomass Using Synthetic Aperture Radar and Multispectral Data

Adam Collingwood,Paul Treitz,Francois Charbonneau,David Atkinson

doi:10.3390/rs6032134

Abstract

Vegetation in the Arctic is often sparse, spatially heterogeneous, and difficult to model. Synthetic Aperture Radar (SAR) has shown some promise in above-ground phytomass estimation at sub-arctic latitudes, but the utility of this type of data is not known in the context of the unique environments of the Canadian High Arctic. In this paper, Artificial Neural Networks (ANNs) were created to model the relationship between variables derived from high resolution multi-incidence angle RADARSAT-2 SAR data and optically-derived (GeoEye-1) Soil Adjusted Vegetation Index (SAVI) values. The modeled SAVI values (i.e., from SAR variables) were then used to create maps of above-ground phytomass across the study area. SAVI model results for individual ecological classes of polar semi-desert, mesic heath, wet sedge, and felsenmeer were reasonable, with r2 values of 0.43, 0.43, 0.30, and 0.59, respectively. When the outputs of these models were combined to analyze the relationship between the model output and SAVI as a group, the r2 value was 0.60, with an 8% normalized root mean square error (% of the total range of phytomass values), a positive indicator of a relationship. The above-ground phytomass model also resulted in a very strong relationship (r2 = 0.87) between SAR-modeled and field-measured phytomass. A positive relationship was also found between optically derived SAVI values and field measured phytomass (r2 = 0.79). These relationships demonstrate the utility of SAR data, compared to using optical data alone, for modeling above-ground phytomass in a high arctic environment possessing relatively low levels of vegetation.

Highlights

Knowledge of the spatial distribution of vegetation cover and phytomass in the High Arctic is becoming increasingly important due to the changing climate of this region
Values or previously modeled above-ground phytomass [9]. These results indicate that the levels of above-ground phytomass are not sufficient for polarimetric methods to be helpful in vegetation modeling for this study area with the available polarimetric scenes, a conclusion further supported by the lack of correlation between other Synthetic Aperture Radar (SAR)-derived polarimetric variables (Table 2)
High resolution optical data were used to facilitate the modeling of above-ground phytomass using

Summary

Introduction

Knowledge of the spatial distribution of vegetation cover and phytomass in the High Arctic is becoming increasingly important due to the changing climate of this region. Remote sensing is the best tool available to accurately map the spatial distribution of above-ground phytomass at the fine scales necessary to distinguish between these vegetation community types. This fine-scale mapping is crucial for accurate carbon budgets and phytomass estimation at the local scale [15], and for accurately scaling up these variables to larger regional scales [16,17]

Methods

Results

Conclusion