Using Landsat TM data to aid the assessment of long-term trends in lake water quality in New Hampshire lakes

Assessing long-term trends in lake water quality is an important aspect of lake management. In the state of New Hampshire (NH), volunteer monitors working with the NH Lakes Lay Monitoring Program (LLMP) have measured lake quality parameters in many of the state´s lakes for one or two decades. These measurements have served as the data bank for both policy decisions and scientific research on lake health. Because of the promise of improved remote sensing platforms for gathering water quality observations on a consistent basis across the state, we examine the potential relationships between remotely sensed observations and in situ water quality measurements, using Landsat TM imagery at a resolution of 30 m. Strong relationships between water clarity (Secchi disk transparency) and Landsat TM bands 1 and 3 have been determined for lakes in the Upper Midwest region. Using the long-term measurements of water quality data in NH lakes (water clarity, chlorophyll a, dissolved organic color, aquatic plant extent), we examine the usefulness beyond the original region of study of the empirical relationships between Landsat TM bands and Secchi disk transparency developed for Midwestern lakes. TM scenes taken during the period 1993-1999 are compared to water quality measurements for approximately 50 lakes in NH. The ability of 30 m spatial resolution imagery to capture temporal and spatial trends in lake water quality in our region is examined.