John Osterberg

An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method

We used the Enhanced Vegetation Index (EVI) from MODIS to scale evapotranspiration (ETactual) over agricultural and riparian areas along the Lower Colorado River in the southwestern US. Ground measurements of ETactual by alfalfa, saltcedar, cottonwood and arrowweed were expressed as fraction of potential (reference crop) ETo (EToF) then regressed against EVI scaled between bare soil (0) and full vegetation cover (1.0) (EVI*). EVI* values were calculated based on maximum and minimum EVI values from a large set of riparian values in a previous study. A satisfactory relationship was found between crop and riparian plant EToF and EVI*, with an error or uncertainty of about 20% in the mean estimate (mean ETactual = 6.2 mm d−1, RMSE = 1.2 mm d−1). The equation for ETactual was: ETactual = 1.22 × ETo-BC × EVI*, where ETo-BC is the Blaney Criddle formula for ETo. This single algorithm applies to all the vegetation types in the study, and offers an alternative to ETactual estimates that use crop coefficients set by expert opinion, by using an algorithm based on the actual state of the canopy as determined by time-series satellite images.

Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

AbstractThe estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (hc), displacement height (d), and roughness length (z0) combined with the LAS weighing function, W(u), alon...

Life History Characteristics of Diorhabda Carinulata Under Various Temperatures

ABSTRACT Tamarisk leaf beetles, Diorhabda spp., have been released in the western United States as a biological control agent for the invasive weed Tamarix spp. There have been a few studies on the life cycle, host preferences, and field observations of Diorhabda; however, their ecophysiological characteristics under various temperature regimes are not clearly understood. In this study, life history characteristics such as growth, fecundity, and mortality of Diorhabda carinulata (Desbrochers), the species established in the Colorado River basin, were investigated under various temperatures. Beetles were housed at various temperatures (room, constant high, and variable high) and their life cycle from eggs to reproductive adult was observed. Body size at various larval and adult stages, as well as their developmental time decreased with increasing temperature. Between the two temperature treatments, beetles at diurnally fluctuating temperature (variable high treatment) grew slower and produced fewer eggs per clutch when compared with the constant high treatment. Despite smaller in size, beetles grew fastest at the constant high temperature and produced most eggs per clutch compared with the other two treatments. Overall, severely high temperatures seem to have a debilitating effect on Diorhabda at early larval stages with nearly 50% mortality. The study has potential implications for the tamarisk beetle biocontrol program in the southwestern United States.