MODIS Global Terrestrial Evapotranspiration (ET) Product (NASA MOD16A2/A3) Collection 5. NASA Headquarters

In the original EOS proposal competition in 1989, Dr. Steve Running proposed and was selected as MODIS Science team member responsible for Leaf area index, evapotranspiration and photosynthesis/net primary production, then designated as MOD 15, 16 and 17. At the ATBD review for at-launch products in 1995, NASA decided to give MOD 15 LA I/FPAR to Dr. Ranga Myneni to provide a more theoretically based algorithm, and Dr. Running was directed to focus on MOD 17 PSN/NPP for the Terra atlaunch data product. MOD 16 ET was not dropped, but was deprioritized. At the EOS recompete in 2003 NASA selected another investigator to build a MOD 16 ET product but this investigation was not renewed in 2007. In the interim Dr. Running and the NTSG group had changed from an energy balance - surface resistance concept to a Penman-Monteith concept, and had greater success building a globally applicable algorithm. Since much of the processing paralleled our MOD 17 product, NTSG tested, then generated initial global ET datasets. In the 2010 renewal competition for the MODIS Science Team, Dr. Running reproposed MOD 16, based on the new algorithm and global ET datasets now developed, and published in refereed journals. Now, with selection of our 2010 renewal proposal complete, we offer the ATBD. This document represents our formal ATBD for establishing this algorithm and dataset as the official MOD 16 Evapotranspiration product

White dwarf-main sequence binaries from LAMOST: the DR1 catalogue

Context. White dwarf-main sequence (WDMS) binaries are used to study several different important open problems in modern astrophysics. Aims. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of WDMS binaries currently known. However, this sample is seriously affected by selection effects and the population of systems containing cool white dwarfs and early-type companions is under-represented.Here we search for WDMS binaries within the spectroscopic data release 1 of the LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow different target selection algorithms. Hence, LAMOST WDMS binaries may be drawn from a different parent population and thus help in overcoming the selection effects incorporated by SDSS on the current observed population. Methods. We develop a fast and efficient routine based on the wavelet transform to identify LAMOST WDMS binaries containing a DA white dwarf and a M dwarf companion, and apply a decomposition/fitting routine to their LAMOST spectra to estimate their distances and measure their stellar parameters, namely the white dwarf effective temperatures, surface gravities and masses, and the secondary star spectral types. Results. We identify 121 LAMOST WDMS binaries, 80 of which are new discoveries, and estimate the sample to be \sim90 per cent complete. The LAMOST and SDSS WDMS binaries are found to be statistically different. However, this result is not due to the different target selection criteria of both surveys, but likely a simple consequence of the different observing conditions. Thus, the LAMOST population is found at considerably shorter distances (\sim50-450 pc) and is dominated by systems containing early-type companions and hot white dwarfs. (abridged)Comment: 14 pages, 8 figures, accepted for publication in A&

A global comparison between station air temperatures and MODIS land surface temperatures reveals the cooling role of forests

Most global temperature analyses are based on station air temperatures. This study presents a global analysis of the relationship between remotely sensed annual maximum LST (LSTmax) from the Aqua/Moderate Resolution Imaging Spectroradiometer (MODIS) sensor and the corresponding site-based maximum air temperature (Tamax) for every World Meteorological Organization station on Earth. The relationship is analyzed for different land cover types. We observed a strong positive correlation between LSTmax and Tamax. As temperature increases, LSTmax increases faster than Tamax and captures additional information on the concentration of thermal energy at the Earth\u27s surface, and biophysical controls on surface temperature, such as surface roughness and transpirational cooling. For hot conditions and in nonforested cover types, LST is more closely coupled to the radiative and thermodynamic characteristics of the Earth than the air temperature (Tair). Barren areas, shrublands, grasslands, savannas, and croplands have LSTmax values between 10°C and 20°C hotter than the corresponding Tamax at higher temperatures. Forest cover types are the exception with a near 1:1 relationship between LSTmax and Tamax across the temperature range and 38°C as the approximate upper limit of LSTmax with the exception of subtropical deciduous forest types where LSTmax occurs after canopy senescence. The study shows a complex interaction between land cover and surface energy balances. This global, semiautomated annual analysis could provide a new, unique, monitoring metric for integrating land cover change and energy balance changes

Web users' language utilization behaviors in China

The paper focuses on the habits of China Web users' language utilization behaviors in accessing the Web. It also seeks to make a general study on the basic nature of language phenomenon with regard to digital accessing. A questionnaire survey was formulated and distributed online for these research purposes. There were 1,267 responses collected. The data were analyzed with descriptive statistics, Chi-square testing and contingency table analyses. Results revealed the following findings. Tagging has already played an important role in Web2.0 communication for China's Web users. China users rely greatly on all kinds of taxonomies in browsing and have also an awareness of them in effective searching. These imply that the classified languages in digital environment may aid Chinese Web users in a more satisfying manner. Highly subject-specific words, especially those from authorized tools, yielded better results in searching. Chinese users have high recognition for related terms. As to the demographic aspect, there is little difference between different genders in the utilization of information retrieval languages. Age may constitute a variable element to a certain degree. Educational background has a complex effect on language utilizations in searching. These research findings characterize China Web users' behaviors in digital information accessing. They also can be potentially valuable for the modeling and further refinement of digital accessing services.</p

Satellite Finds Highest Land Skin Temperatures on Earth

The location of the hottest spot on Earth has undoubtedly been an interesting curiosity for centuries. Even with the advent of the instrumental temperature record around the year 1850, the location of the hottest spot on Earth has continued to be the subject of debate and controversy. In 1913, the weather station at Furnace Creek in Death Valley National Park, California, measured an air temperature of 56.7°C (134.1°F) and claimed the title of “hottest place on Earth.” Nine years later in El Azizia, Libya, an air temperature of 57.8°C (136°F) was recorded on land owned by an Italian farmer and the title of the “hottest place on Earth” moved from the United States to Libya. The 1922 air temperature measurement from El Azizia has never been surpassed. In reality, finding the hottest spot on Earth based on scattered site-based air temperature measurements is a limited approach due to the poor spatial coverage of the instruments where measurements are taken compared with Earth’s expansive barren deserts where the hottest conditions occur. The World Meteorological Organization (WMO) has approximately 11,119 weather stations on Earth’s land surface collecting surface temperature observations (ftp://ftp.ncdc.noaa.gov/pub/data/gsod/2010). When compared to the 144.68 million km2 of land surface, that’s one station every 13,012 km2. The Earth’s hot deserts, such as the Sahara, the Gobi, the Sonoran, and the Lut, are climatically harsh and so remote that access for routine measurements and maintenance of a weather station is impractical. The majority of Earth’s potentially hottest spots are simply not being directly measured by ground-based instruments. Satellites provide a continuous view of Earth’s surface, allowing equal observation of the most remote areas and the most accessible. However, satellites do not measure the near-surface air temperature; instead they measure the radiometric surface temperature, or skin temperature, a different physical parameter

Sensitivity of Moderate Resolution Imaging Spectroradiometer (MODIS) Terrestrial Primary Production to the Accuracy of Meteorological Reanalyses

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA\u27s satellites, Terra and Aqua, dramatically improves our ability to accurately and continuously monitor the terrestrial biosphere. MODIS information is used to estimate global terrestrial primary production weekly and annually in near-real time at a 1-km resolution. MODIS terrestrial primary production requires daily gridded assimilation meteorological data as inputs, and the accuracy of the existing meteorological reanalysis data sets show marked differences both spatially and temporally. This study compares surface meteorological data sets from three well-documented global reanalyses, NASA Data Assimilation Office (DAO), European Centre for Medium-Range Weather Forecasts (ECMWF) (ERA-40) and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis 1, with observed weather station data and other gridded data interpolated from the observations, to evaluate the sensitivity of MODIS global terrestrial gross and net primary production (GPP and NPP) to the uncertainties of meteorological inputs both in the United States and the global vegetated areas. NCEP tends to overestimate surface solar radiation, and underestimate both temperature and vapor pressure deficit (VPD). ECMWF has the highest accuracy but its radiation is lower in tropical regions, and the accuracy of DAO lies between NCEP and ECMWF. Biases in temperature are mainly responsible for large VPD biases in reanalyses. MODIS NPP contains more uncertainties than GPP. Global total MODIS GPP and NPP driven by DAO, ECMWF, and NCEP show notable differences (\u3e20 Pg C/yr) with the highest estimates from NCEP and the lowest from ECMWF. Again, the DAO results lie somewhere between NCEP and ECMWF estimates. Spatially, the larger discrepancies among reanalyses and their derived MODIS GPP and NPP occur in the tropics. These results reveal that the biases in meteorological reanalyses can introduce substantial error into GPP and NPP estimations, and emphasize the need to minimize these biases to improve the quality of MODIS GPP and NPP products

Dynamics of MODIS evapotranspiration in South Africa

This paper describes the dynamics of evapotranspiration (ET) in South Africa using MOD16 ET satellite-derived data, and analyses the inter-dependency of variables used in the ET algorithm of Mu et al. (2011). Annual evapotranspiration is strongly dependent on rainfall and potential evapotranspiration (PET) in 4 climatically different regions of South Africa. Average ET in South Africa (2000–2012) was estimated to be 303 mm·a-1 or 481.4 x 109 m3·a1 (14% of PET and 67% of rainfall), mainly in the form of plant transpiration (T, 53%) and soil evaporation (Soil E, 39%). Evapotranspiration (ET) showed a slight tendency to decrease over the period 2000–2012 in all climatic regions, except in the south of the country (winter rainfall areas), although annual variations in ET resulted in the 13-year trends not being statistically significant. Evapotranspiration (ET) was spatially dependent on PET, T and vapour pressure deficit (VPD), in particular in winter rainfall and arid to semi-arid climatic regions. Assuming an average rainfall of 450 mm·a-1, and considering current best estimates of runoff (9% of rainfall), groundwater recharge (5%) and water withdrawal (2%), MOD16 ET estimates were about 15% short of the water balance closure in South Africa. The ET algorithm can be refined and tested for applications in restricted areas that are spatially heterogeneous and by accounting for soil water supply limiting conditions

Contribution of increasing CO2 and climate change to the carbon cycle in China\u27s ecosystems

Atmospheric CO2 and China\u27s climate have changed greatly during 1961–2000. The influence of increased CO2 and changing climate on the carbon cycle of the terrestrial ecosystems in China is still unclear. In this article we used a process-based ecosystem model, Biome-BGC, to assess the effects of changing climate and elevated atmospheric CO2 on terrestrial China\u27s carbon cycle during two time periods: (1) the present (1961–2000) and (2) a future with projected climate change under doubled CO2 (2071–2110). The effects of climate change alone were estimated by driving Biome-BGC with a fixed CO2 concentration and changing climate, while the CO2 fertilization effects were calculated as the difference between the results driven by both increasing CO2 and changing climate and those of variable climate alone. Model simulations indicate that during 1961–2000 at the national scale, changes in climate reduced carbon storage in China\u27s ecosystems, but increasing CO2 compensated for these adverse effects of climate change, resulting in an overall increase in the carbon storage of China\u27s ecosystems despite decreases in soil carbon. The interannual variability of the carbon cycle was associated with climate variations. Regional differences in climate change produced differing regional carbon uptake responses. Spatially, reductions in carbon in vegetation and soils and increases in litter carbon were primarily caused by climate change in most parts of east China, while carbon in vegetation, soils, and litter increased for much of west China. Under the future scenario (2071–2110), with a doubling CO2, China will experience higher precipitation and temperature as predicted by the Hadley Centre HadCM3 for the Intergovernmental Panel on Climate Change Fourth Assessment. The concomitant doubling of CO2 will continue to counteract the negative effects of climate change on carbon uptake in the future, leading to an increase in carbon storage relative to current levels. This study highlights the role of CO2 fertilization in the carbon budget of China\u27s ecosystems, although future studies should include other important processes such as land use change, human management (e.g., fertilization and irrigation), environmental pollution, etc

A New Satellite-Based Methodology for Continental-Scale Disturbance Detection

The timing, location, and magnitude of major disturbance events are currently major uncertainties in the global carbon cycle. Accurate information on the location, spatial extent, and duration of disturbance at the continental scale is needed to evaluate the ecosystem impacts of land cover changes due to wildfire, insect epidemics, flooding, climate change, and human-triggered land use. This paper describes an algorithm developed to serve as an automated, economical, systematic disturbance detection index for global application using Moderate Resolution Imaging Spectroradiometer (MODIS)/Aqua Land Surface Temperature (LST) and Terra/MODIS Enhanced Vegetation Index (EVI) data from 2003 to 2004. The algorithm is based on the consistent radiometric relationship between LST and EVI computed on a pixel-by-pixel basis. We used annual maximum composite LST data to detect fundamental changes in land–surface energy partitioning, while avoiding the high natural variability associated with tracking LST at daily, weekly, or seasonal time frames. Verification of potential disturbance events from our algorithm was carried out by demonstration of close association with independently confirmed, well-documented historical wildfire events throughout the study domain. We also examined the response of the disturbance index to irrigation by comparing a heavily irrigated poplar tree farm to the adjacent semiarid vegetation. Anomalous disturbance results were further examined by association with precipitation variability across areas of the study domain known for large interannual vegetation variability. The results illustrate that our algorithm is capable of detecting the location and spatial extent of wildfire with precision, is sensitive to the incremental process of recovery of disturbed landscapes, and shows strong sensitivity to irrigation. Disturbance detection in areas with high interannual variability of precipitation will benefit from a multiyear data set to better separate natural variability from true disturbance