Remote sensing technology has become the primary tool for ecological research at large scales, but there is a major problem in differentiating between different spectra for the same vegetation and the same spectra for different vegetation, when classifying saltmarsh vegetation in remotely sensed images in Shanghai. The spectral characteristics of the saltmarsh vegetation canopy, including four main communities: Phragmites australis community, Spartina alterniflora community, Scirpus mariqueter community and Carex scabrifolia community, were measured by a ground FieldSpecＴＭ Pro JR spectroradiometer, in the Chongming Dongtan Natural Reserve. The spectral data were converted to the reflectance curves, and their first derivative curves between 350nm and 1000nm were calculated. The differences in the reflectance and first derivative curves were then analyzed, with particular attention paid to the characteristics in the bands of visible, near infrared, “green peak" and “red edge".
The results from this study showed that the different saltmarsh communities had different and rather unique spectral characteristics during the three seasons studied (spring, summer and autumn). As well, the differences among the spectral characteristics during the three seasons for these four communities were not the same. It is proposed that the optimal strategy for classifying the saltmarsh vegetation may be through the integration and analysis of multi-seasonal images. The results from this study can serve as a tool for monitoring the distribution pattern and dynamics of the exotic plant Spartina alterniflora, as well as to provide a basis for the judgment and interpretation of the hyper-spectral image, and for the mapping of saltmarsh vegetation.