@inbook {KNZ00296, title = {Satellite remote sensing and field experiments}, booktitle = {Remote Sensing of Biosphere Functioning}, year = {1990}, pages = {169 -201}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {New York, NY}, abstract = {

The past few years have seen an increasing pressure brought to bear on biologists to apply their research efforts to larger spatial scales. The motivation for this pressure has scientific as well as sociopolitical roots. First, from the science viewpoint, it has become apparent that satellite-based and atmospheric observing techniques can allow researchers a different view of biospheric functioning by spatially integrating the effects of biospheric states and fluxes, respectively, at moderate cost

}, keywords = {LTER-KNZ}, author = {Sellers, P.J. and Hall, F.G. and Strebel, D.E. and Asrar, G.A. and Murphy, R.E.}, editor = {Hobbs, R.J. and Mooney, H.A.} } @article {KNZ00214, title = {Measuring and modeling spectral characteristics of a tallgrass prairie}, journal = {Remote Sensing of the Environment}, volume = {27}, year = {1989}, pages = {143 -155}, abstract = {

This study was conducted to evaluate the diurnal and seasonal, spectral reflectance characteristics of burned and unburned areas of a tallgrass prairie, based on field measurements and models of radiation transport in plant canopies. Burning of the senescent vegetation, resulting from the previous years\&$\#$39; growth, is a common management practice, which results in improved productivity and affects the succession of grass species. The burned and unburned grass canopies showed distinctly different, diurnal and seasonal, spectral reflectance characteristics in the visible and infrared regions of the spectrum. These were attributed to the differences in development of the two plant canopies and the azimuthal differences in sensor-sun-canopy positions during field measurements of spectral reflectance. The radiation transfer model properly simulated the diurnal spectral behavior of the two canopies. The simulated, seasonal, spectral reflectance values for the unburned grass canopy were greater than the measured ones, because of limitations in proper representation of the layer of senescent vegetation in the model

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1016/0034-4257(89)90014-X}, author = {Asrar, G.A. and Myneni, R.B. and Li, Y. and Kanemasu, E.T.} } @article {KNZ00207, title = {The first ISLSCP field experiment (FIFE)}, journal = {Bulletin of the American Meteorological Society}, volume = {69}, year = {1988}, pages = {22 -27}, abstract = {

The International Satellite Land Surface Climatology Project (ISLSCP) was initiated to address the research problems associated with interpretation and exploitation of satellite data over the earth\&$\#$39;s land surface. As the project developed, it was recognized that these objectives could not be attained unless there was also a clearer understanding of the biological controls acting on land-surface-atmosphere fluxes

}, keywords = {LTER-KNZ}, doi = {10.1175/1520-0477(1988)069\<0022:TFIFE\>2.0.CO;2}, author = {Sellers, P.J. and Hall, F.G. and Asrar, G.A. and Strebel, D.E. and Murphy, R.E.} } @article {KNZ00168, title = {Radiative surface temperatures of the burned and unburned areas in a tallgrass prairie}, journal = {Remote Sensing of the Environment}, volume = {24}, year = {1988}, pages = {447 -457}, abstract = {

This study was comducted in a natrul tallgrass prairie area in the Flint Hills of Kansas. Our objective was to evaluate the surface radiative temperatures of burned and unburned treatments of the grassland as a means of delineating the areas covered by each treatment. Burning is used to remove the senescent vegetation resulting from the previous year\&$\#$39;s growth. Surface temperatures were obtained in situ andby an airborne scanner. Burned and unburned grass canopies had distinctly different diurnal surface radiative temperatures. Measurements of surface energy balance components revealed a difference in partitioning of of the available energy between the two canopies, which resulted in the difference in their measured surface temperatures. The magnitude of this difference is dependent of the time of measurements and topographic conditions

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1016/0034-4257(88)90018-1}, author = {Asrar, G.A. and Harris, T.R. and Lapitan, R.L. and Cooper, D.I.} } @article {KNZ00202, title = {Results from the push broom microwave radiometer flights over the Konza Prairie in 1985}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, volume = {26}, year = {1988}, pages = {590 -596}, abstract = {

There were four flights of the NASA C-130 aircraft carrying the Push Broom Microwave Radiometer (PBMR) over the Konza Prairie Research Natural Area in eastern Kansas in 1985. Their objective was to observe surface soil moisture variations with the PBMR. The radiometer operates at the 21-cm wavelength and has four beams that sweep out a swath of about 1.2 times the aircraft altitude. The resolution of each beam is 0.3 times the altitude. At the time of the flights the soil conditions ranged from very wet to moist and the microwave emission expressed as brightness temperatures for the burned watersheds ranged from below 200 to about 245 K. The brightness temperatures were correlated (r2 = 0.5) with surface moisture measurements and the slope of the regression is in good agreement with prior results over other grasslands. However, for the unburned watersheds the brightness temperatures were around 270 K and roughly independent of the soil moisture conditions. In these unburned watersheds, a buildup of a thatch layer serves as highly emissive layer above the soil, causing high brightness, especially when wet

}, keywords = {LTER-KNZ}, doi = {10.1109/36.7684}, author = {Schmugge, T.J. and Wang, J.R. and Asrar, G.A.} } @proceedings {KNZ00159, title = {Airborne multispectral observations over burned and unburned prairies}, year = {1987}, pages = {203 -207}, address = {Ann Arbor, MI}, abstract = {

One of the ongoing studies at the Konza Prairie Natural Area (KPNA) in central Kansas is that of determining the effects periodic burning has on the native grassland ecosystem. In this study, watersheds are burned at intervals from one year to ten years or not at all. The Evapotransiration Laboratory at Kansas State University has been studying the multispectral response of burned and unburned watersheds using truck mounted raiometers and microwave scatterometers since 1983. In June 1985, there was a series of 5 flights with the NASA C-130 aircraft over the KPNA. On board the aircraft was the NS001 multispectral scanner, also known as the thematic mapper simulator. It has 7 visible and near IR channels and a thermal IR channels, whose spectral bands were chosen to simulate the thematic mapper on Landsat\&$\#$39;s 4 and 5. The 21-cm Pushbroom Microwave Radiometer (PBMR) was also on board the aircraft for soil and moisture observations. In addition several L- Band SAR images from the NASA CV-990 aircraft were obtained during this period. The spectral differences between the burned and unburned watersheds were clearly observable in all spectral bands including the thermal IR and the microwave. The normalized difference vegetation index (NDVI) using TM bands 3 and 4 was calculated. Values of less than 0.5 were obtained for the unburned watersheds which contained a mixture of senescent and green vegetaion. The NDVI values for the burned watersheds which contained only green vegetation were greater than 0.6. In the thermal IR, 3 to 4 degree Celsius temperature differences between the two treatments were observed at about 2:00 p.m. LST with the burned watersheds being cooler. Large differences between the two treatments were observed in the microwave emissivities derived from the PBMR data. These are attributed to the build-up of a layer of senescent vegetation on the soil surface in the unburned and ungrazed watersheds

}, keywords = {LTER-KNZ}, author = {Schmugge, T.J. and Kanemasu, E.T. and Asrar, G.A.} } @article {KNZ00130, title = {Assessing grassland biophysical characteristics from spectral measurements}, journal = {Remote Sensing of the Environment}, volume = {20}, year = {1986}, pages = {141 -152}, abstract = {

Remote sensing offers a potential alternative to tedious hand sampling as a means of monitoring vegetation condition and estimating productivity over large areas of grasslands. This sutdy was conducted to assess the use of spectral reflectance measurements in estimating grass canopy leaf area index (LAI) and total above ground green phytomass. Spectral reflectance measurements were made on a tallgrass prairie during 1983 and 1984 with two multiband radiometers. Green leaf-area index and dry matter accumulations (green above-ground phytomass) were measured on the area monitored by the radiometer. Three indices-near infrared to red ratio, greenness, and normalized difference-were computed from spectral reflectance data. The direct relationships between these special reflectance indices and grass biophysical parameters (LAI and phytomass) were site-dependent and year-specific. Indirect methods of estimating LAI and phytomass from estimates of absorbed, phytosynthetically active radiation, based on measurements of grass canopy spectral reflectance, were found to be more consistent across treatments for the two years of this study

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1016/0034-4257(86)90019-2}, author = {Weiser, R.L. and Asrar, G.A. and Miller, G.P. and Kanemasu, E.T.} } @article {KNZ00110, title = {Distinguishing among tallgrass prairie cover types from measurements of multispectral reflectance}, journal = {Remote Sensing of the Environment}, volume = {19}, year = {1986}, pages = {159 -169}, abstract = {

The heterogeneity in surface cover caused by management practices or natural events complicates monitoring the conditions of grasslands and asseessing their productivity by remote sensing techniques. Statistical procedures were sought that would allow different grassland surface cover types (bare soil,senescent vegetation, and green vegetation) to be distinguished by using measurements of grassland multispectral reflectance. Two procedures, discriminant functions and canonical discriminant analysis, were found suitable for achieving this objective. Linear classification functions and canonical variables were derived, which distinguish between the three cover types. A comparison between two sensor systems, a Barnes multiband radiometer and an Exotech radiometer that simulates the Landsatthematic mapper (TM) and multispectral scanner (MSS) bands, respectively, showed that the separability among the three cover types was substantially improved by the additional and improved spectral features of the Barnes radiometer

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1016/0034-4257(86)90069-6}, author = {Asrar, G.A. and Weiser, R.L. and Johnson, D.E. and Kanemasu, E.T. and Killeen, J.M.} } @article {KNZ00109, title = {Light interception and leaf area estimates from measurements of grass canopy reflectance}, journal = {IEEE Transactions of Geoscience and Remote Sensing}, volume = {GE-24}, year = {1986}, pages = {76 -82}, abstract = {

Grassland is a major component of the Earth\&$\#$39;s available land. The vast area and remoteness of this ecosystem makes it difficult to assess its condition and monitor productivity by traditional methods. Remote sensing potentially offers a rapid nondestructive approach for monitoring such ecosystems. A study was carried out in a tallgrass prairie site near Manhattan, Kansas, during the 1983 and 1984 seasons to investigate the feasibility of estimating light interception and green leaf area index (LAI) from measurements of canopy multispectral reflectance. Greenness (Gn) index was found to be strongly correlated with intercepted photosynthetically active radiation (PAR). Two methods, a direct regression (RGR) and an indirect approach (IND), were used to estimate LAI form Gn index. The LAI values estimated by RGR method were consistently lower than the measured ones; however, good agreement was obtained between the LAI values estimated by IND method and the measured LAI. This suggests that Gn transformation of canopy spectral reflectance is more closely related to the fraction of intercepted PAR by green foliage than the quantity of green LAI

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1109/TGRS.1986.289590}, author = {Asrar, G.A. and Kanemasu, E.T. and Miller, G.P. and Weiser, R.L.} }