High and low resolution TM data for the assessment of herbage and sward characteristics in small fields

Abstract

The smallfield pattern characteristic of the Northern Ireland landscape necessitates the use of high resolution remotely-sensed imagery in grassland studies. In August 1986, 5 m resolution ATM and 30 m resolution TM data was collected from a grassland area in Northern Ireland. Herbage mass, sward surface height and botanical characteristics were assessed for approximately 120 fields in the overfly area. Correlations between digital numbers (DN) in three wavebands for both resolutions from commonly sampled fields were poor as a result of small field size and poor overlap of pixel area sampled. Variability and error associated with ground data probably masked any effect of small field size. Height, mass and percentage dead matter were the sward variables predicted with most accuracy by DN but most correlations were low and 5 m resolution was better than 30 m resolution. Both sets of imagery appear to have more potential to improve and quantify grassland classifications rather than provide absolute values for useful sward parameters.