Dielectric Constant and Water Potential Measurements During the Forest Ecosystem Dynamics - Multisensor Aircraft Campaign

Forest Ecosystem Dynamics Multisensor Airborne Campaign (FED MAC):
Dielectric and Pressure Bomb Data for Hemlock and Red Spruce

The Biospheric Sciences Branch (formerly Earth Resources Branch) within the Laboratory for Terrestrial Physics at NASA's Goddard Space Flight Center and associated University investigators are involved in a research program entitled Forest Ecosystem Dynamics (FED) which is fundamentally concerned with vegetation change of forest ecosystems at local to regional spatial scales (100 to 10,000 meters) and temporal scales ranging from monthly to decadal periods (10 to 100 years). The nature and extent of the impacts of these changes, as well as the feedbacks to global climate, may be addressed through modeling the interactions of the vegetation, soil, and energy components of the boreal ecosystem.

This dataset contains the dielectric and pressure bomb data for hemlock and red spruce. All data sets contain just the raw data. The pressure bomb measurements appear to be reliable. The dielectric data needs to be calibrated for both the P- and C- band probes.

The relative dielectric constant measurements were made using portable dielectric probes. The probe calculates the dielectric constant by measuring the change in impedance of the capacitor in contact with the test material. The magnitude and phase of the reflection coefficient are measured and used with calibration factors to determine the relative dielectric constant.

Water potential measurements were made by placing branch samples in a Scholander pressure bomb. Pruning poles were used to cut the branches from the mid-canopy. Pressure bomb readings were taken from 7 a.m. until 4:30 p.m. at approximately 30-minute intervals, and were performed on two to three branch samples to ensure accuracy.