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Ground Measurements (ground + measurement)
Selected AbstractsSite-level evaluation of satellite-based global terrestrial gross primary production and net primary production monitoringGLOBAL CHANGE BIOLOGY, Issue 4 2005David P. Turner Abstract Operational monitoring of global terrestrial gross primary production (GPP) and net primary production (NPP) is now underway using imagery from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Evaluation of MODIS GPP and NPP products will require site-level studies across a range of biomes, with close attention to numerous scaling issues that must be addressed to link ground measurements to the satellite-based carbon flux estimates. Here, we report results of a study aimed at evaluating MODIS NPP/GPP products at six sites varying widely in climate, land use, and vegetation physiognomy. Comparisons were made for twenty-five 1 km2 cells at each site, with 8-day averages for GPP and an annual value for NPP. The validation data layers were made with a combination of ground measurements, relatively high resolution satellite data (Landsat Enhanced Thematic Mapper Plus at ,30 m resolution), and process-based modeling. There was strong seasonality in the MODIS GPP at all sites, and mean NPP ranged from 80 g C m,2 yr,1 at an arctic tundra site to 550 g C m,2 yr,1 at a temperate deciduous forest site. There was not a consistent over- or underprediction of NPP across sites relative to the validation estimates. The closest agreements in NPP and GPP were at the temperate deciduous forest, arctic tundra, and boreal forest sites. There was moderate underestimation in the MODIS products at the agricultural field site, and strong overestimation at the desert grassland and at the dry coniferous forest sites. Analyses of specific inputs to the MODIS NPP/GPP algorithm , notably the fraction of photosynthetically active radiation absorbed by the vegetation canopy, the maximum light use efficiency (LUE), and the climate data , revealed the causes of the over- and underestimates. Suggestions for algorithm improvement include selectively altering values for maximum LUE (based on observations at eddy covariance flux towers) and parameters regulating autotrophic respiration. [source] Early findings in comparison of AMSR-E/Aqua L3 global snow water equivalent EASE-grids data with in situ observations for Eastern TurkeyHYDROLOGICAL PROCESSES, Issue 15 2008A. Emre Tekeli Abstract Microwave remote sensing (RS) enables the direct determination of snow water equivalent (SWE), which is an important snow parameter for water resources management. The accuracy of remotely sensed SWE values has always been a concern. Previous studies evaluated global SWE monitoring. However, regional effects such as vegetation, snow grain size, snow density and local meteorological conditions may lead to uncertainties. Thus, regional validation studies that quantify and help to understand these uncertainties and possible error sources are important both for algorithm development and accurate SWE computation. In this study, data of Advanced Microwave Scanning Radiometer (AMSR-E)/Aqua level 3 global SWE Equal Area Scalable Earth (EASE) Grids are compared with ground measurements for 2002,2003 winter period for Eastern Turkey, which includes the headwaters of the Euphrates and Tigris rivers and is fed largely from snowmelt. Thus, accurate determination of SWE is important in optimum resource management for both Turkey and downstream nations. Analyses indicated that AMSR-E generally overestimated SWE in early season. As winter progressed, higher in situ SWE values with respect to AMSR-E were observed which led to underestimation by AMSR-E. The differences between AMSR-E and in situ SWE varied between , 218 and 93 mm. Use of in situ snow densities lead the correlation coefficient between AMSR-E and in situ SWE to increase from 0·10 to 0·32. Underestimation of SWE by AMSR-E occurs after some warm periods, while overestimations occur following refreezing. On rainy days or some days after precipitation within the warm periods, zero AMSR-E SWE values are observed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hydrology as a policy-relevant scienceHYDROLOGICAL PROCESSES, Issue 16 2004Kuniyoshi Takeuchi Abstract Water is now a global political agenda and water science is part of it. The United Nations Millennium Development Goals (MDGs) in 2000, the World Summit on Sustainable Development in 2002, the 3rd World Water Forum and Ministerial Conference in Kyoto in 2003 and the G8 Summit in Evian in 2003 were all concerned about urgent global water issues and call for international scientific research collaboration. Hydrology is responding to such political commitments with various scientific initiatives that include the International Association of Hydrological Sciences (IAHS) Predictions in Ungauged Basins (PUB), the Global Energy and Water Circulation Experiments (GEWEX) Coordinated Enhanced Observation Period (CEOP), and the Global Water Systems Project (GWSP). These initiatives will play key roles in the implementation of the new intergovernmental project, Global Earth Observing System of Systems, under preparation by Global Observation Summits from 2003 to 2005. In order to achieve the MDGs, hydrological science has to play a major role supporting policy makers by overcoming methodological obstacles and providing the necessary information. This paper emphasizes that: the availability of ground measurements is a limiting factor that prevents the full use of scientific knowledge; hydrology has to integrate and downscale the various global information into local-scale information useful for river basin management; as the availability of professional personnel is in critical short supply, in addition to funds needed, to achieve the MDGs any scientific research should always accompany capacity-building programmes to close the science divide between developed and developing nations. Copyright © 2004 John Wiley & Sons, Ltd. [source] Current Loads of Coarse Woody Debris on Southeastern Australian Floodplains: Evaluation of Change and Implications for RestorationRESTORATION ECOLOGY, Issue 4 2002Ralph MacNally Abstract We evaluated the status of coarse woody debris (CWD, fallen wood) on floodplains of the southern Murray-Darling basin of southeastern Australia. The floodplains are dominated floristically by the river red gum Eucalyptus camaldulensis. Aerial survey techniques were used to estimate the amounts of woody debris within 200 m of the channels along 2,442 km of 11 rivers of the system, including the Murray and Darling Rivers and the Darling Anabranch. Aerially based indices were converted into wood volumes by using ground-truthing at a selection of sites; there was a strong correlation between index values and measured wood volume densities. For thickly forested sites such as Barmah, Gunbower Island, and the Ovens floodplains, the aerial method was not useful, so ground measurements at randomly positioned sites within the forests were used. Volumes were translated into mass by using conversion factors drawn from the literature. We estimated that total tonnage on approximately 221,000 ha of floodplain forests was 4.175 ± 0.579 × 106 tonne. In the larger forested blocks (>7,000 ha), mean wood densities ranged between approximately 12 tonne/ha on the lower Goulburn up to approximately 24 tonne/ha at Barmah State Forest. The area-weighted mean for the entire area was approximately 19 tonne/ha. A main purpose of the research was to place these figures into an historical perspective to evaluate implications for restoration. A thorough search of historical documentation revealed that there are no extant data upon which to estimate pre-European settlement levels. We used information from an apparently undisturbed "unmanaged" site in the Millewa forests of southern New South Wales as a basis. Wood density there corresponded to a mean figure of 125 tonne/ha wood-mass density. By using this figure we estimate that CWD levels on the southern Murray-Darling basin may be of the order of 15% of pre-European settlement levels. Full restoration of the 221,000 ha surveyed would require 23.5 ± 0.579 × 106 tonne, which is equivalent to about 600,000 mature (1 m diameter at breast height) river red gum trees or the amount of timber derived from clear felling about 115,000 ha of river red gum forest at current stocking levels. We discuss the implications of this massive deficit and possible short- and long-term solutions. [source] Scavenging efficiency of rainfall on black carbon aerosols over an urban environmentATMOSPHERIC SCIENCE LETTERS, Issue 3 2005K. Madhavi Latha Abstract Black carbon (BC) aerosols are the optically absorbing part of carbonaceous aerosols that have significantly different optical and radiative properties. The present study addresses the estimation of black carbon aerosol scavenging coefficient by using ground-based measurements over an urban environment of India, namely, Hyderabad. Extensive ground measurements of black carbon have been carried out during January to December 2004 over a tropical urban environment of Hyderabad. Seasonal variations of black carbon aerosol mass concentration showed high values during dry season and low values during monsoon season. The diurnal variations of BC suggest that the concentrations increased by a factor of ,2 during morning and evening hours compared to afternoon hours. Drastic reduction in black carbon aerosol loading has been observed during rainy days. The statistical fit between black carbon aerosol mass concentration and rainfall suggests the reduction of ,3.6 µg/m3 in atmospheric black carbon aerosol loading for every 1-mm increase in rainfall intensity over the study area. The scavenging coefficient of black carbon aerosols is found to be 1.64 × 10,5 s,1. © Crown Copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source] Temporal stability of an NDVI-LAI relationship in a Napa Valley vineyardAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2 2003LEE F. JOHNSON Abstract Remotely sensed values for normalised difference vegetation index (NDVI) were derived periodically from high-resolution Ikonos satellite images during the 2001 growing season, and compared with ground measurements of vineyard leaf area index (LAI) during that same period. These two derived variables were strongly related in six vineyard blocks on each of four occasions (R2= 0.91 to 0.98). Linear regression equations relating these two derived variables did not differ significantly by time-step, and a single equation accounted for 92 per cent of the variance in the combined dataset. Such temporal stability in that relationship opens the possibility of transforming NDVI maps to LAI units, at least on a localised basis, and minimising (or even eliminating) subsequent ground calibration. This reduction in fieldwork would then decrease information cost for viticulturists who wish to monitor LAI sequentially within season, or who wish to track year-to-year changes in climax LAI with a single image collected annually. To take advantage of this cost reduction, temporal consistency in spectral data values comprising NDVI must be assured. This present paper addresses that issue. [source] | ||||||||||