ASTER User's Guide - NASA

ASTER Users Handbookwind direction, air temperature, relative humidity), full radiation station (long and shortwaveradiation up and down), a shadow band radiometer and an all sky camera. The shadow bandradiometer provides information on total water vapor and aerosol optical depth.Figure 22: Field measurements at the US Coast Guard.Measurements of algal growth rate using 14 C, nutrients (N, P), chlorophyll, phytoplankton,zooplankton, light, temperature and secchi disk transparency are also made tri-monthly at theIndex station (Figure 10) and monthly samples for all constituents except algal growth and lightare made at the Mid-lake station (Figure 20). Many samples are taken annually around the TahoeBasin to examine stream chemistry and snow and atmospheric deposition constituents.11.2.4 Using ASTER to measure water clarityCurrently the decline in water clarity at Lake Tahoe is measured using a secchi disk – a whitedisk that is lowered into the water until it is no longer visible. The UC Davis Tahoe ResearchGroup have been making secchi disk measurements since the mid 60’s at two locations on thelake (Midlake and Index – see Figure 20). Such measurements have been used to monitor thedecline in clarity from a maximum of 35 m when measurements began, to the current low of 20m. These measurements are crucial for monitoring temporal changes in clarity but provide little48