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Full-Text Articles in Physical Sciences and Mathematics
Satellite-Observed Photosynthetic Trends Across Boreal North America Associated With Climate And Fire Disturbance, Scott J. Goetz, Andrew Godard Bunn, Gregory J. Fiske, Richard A. Houghton
Satellite-Observed Photosynthetic Trends Across Boreal North America Associated With Climate And Fire Disturbance, Scott J. Goetz, Andrew Godard Bunn, Gregory J. Fiske, Richard A. Houghton
Environmental Sciences Faculty and Staff Publications
We analyzed trends in a time series of photosynthetic activity across boreal North America over 22 years (1981 through 2003). Nearly 15% of the region displayed significant trends, of which just over half involved temperature-related increases in growing season length and photosynthetic intensity, mostly in tundra. In contrast, forest areas unaffected by fire during the study period declined in photosynthetic activity and showed no systematic change in growing season length. Stochastic changes across the time series were predominantly associated with a frequent and increasing fire disturbance regime. These trends have implications for the direction of feedbacks to the climate system …
A Handheld Polarimeter For Aerosol Remote Sensing, James W. Frost, Fouad Nasraddine, J. Rodriguez, I. Andino, Brian Cairns
A Handheld Polarimeter For Aerosol Remote Sensing, James W. Frost, Fouad Nasraddine, J. Rodriguez, I. Andino, Brian Cairns
Publications and Research
In this paper we show how measurements made by a simple handheld polarimeter in conjunction with automated sunsky radiometers can be used to effectively constrain the real part of the complex refractive index of aerosols. We find that even measurements over a limited angular range near 90° scattering angle are sufficient for this purpose. We also note that because of the effect of surface reflectance on the observed degree of linear polarization (DOLP) it is sensible to select spectral bands for these measurements for which the surface is relatively dark and homogeneous (i.e. wavelengths shorter than 700 nm are to …
Changes In Summer Irrigated Crop Area And Water Use In Southeastern Turkey From 1993 To 2002: Implications For Current And Future Water Resources, Mutlu Ozdogan, Curtis E. Woodcock, Guido D. Salvucci, Hüseyin Demir
Changes In Summer Irrigated Crop Area And Water Use In Southeastern Turkey From 1993 To 2002: Implications For Current And Future Water Resources, Mutlu Ozdogan, Curtis E. Woodcock, Guido D. Salvucci, Hüseyin Demir
United States National Aeronautics and Space Administration: Publications
Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based …
Characterizing The Landscape Dynamics Of An Invasive Plant And Risk Of Invasion Using Remote Sensing, Bethany Bradley, John F. Mustard
Characterizing The Landscape Dynamics Of An Invasive Plant And Risk Of Invasion Using Remote Sensing, Bethany Bradley, John F. Mustard
Environmental Conservation Faculty Publication Series
Improved understanding of the spatial dynamics of invasive plant species may lead to more effective land management and reduced future invasion. Here, we identified the spatial extents of nonnative cheatgrass (Bromus tectorum) in the north central Great Basin using remotely sensed data from Landsat MSS, TM, and ETM+. We compared cheatgrass extents in 1973 and 2001 to six spatially explicit landscape variables: elevation, aspect, hydrographic channels, cultivation, roads, and power lines. In 2001, Cheatgrass was 10% more likely to be found in elevation ranges from 1400 to 1700 m (although the data suggest a preferential invasion into lower elevations by …
Microwave Backscatter Modeling Of Erg Surfaces In The Sahara Desert, Haroon Stephen, David G. Long
Microwave Backscatter Modeling Of Erg Surfaces In The Sahara Desert, Haroon Stephen, David G. Long
Public Policy and Leadership Faculty Publications
The Sahara Desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (σ°) modulation with azimuth angle (f). We use σ° measurements observed at various incidence angles and f from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission's Precipitation Radar to model the σ° response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes …
Modeling Microwave Emissions Of Erg Surfaces In The Sahara Desert, Haroon Stephen, David G. Long
Modeling Microwave Emissions Of Erg Surfaces In The Sahara Desert, Haroon Stephen, David G. Long
Public Policy and Leadership Faculty Publications
Sand seas (ergs) of the Sahara are the most dynamic parts of the desert. Aeolian erosion, transportation, and deposition continue to reshape the surface of the ergs. The large-scale features (dunes) of these bedforms reflect the characteristics of the sand and the long-term wind. Radiometric emissions from the ergs have strong dependence on the surface geometry. We model the erg surface as composed of tilted rough facets. Each facet is characterized by a tilt distribution dependent upon the surface roughness of the facet. The radiometric temperature (T(b)) of ergs is then the weighted sum of the T(b) from all the …