Xin-Zhai Tang

Total Nitrogen Concentrations in Surface Water of Typical Agro- and Forest Ecosystems in China, 2004-2009

We assessed the total nitrogen (N) concentrations of 28 still surface water (lake and pond), and 42 flowing surface water (river), monitoring sites under 29 typical terrestrial ecosystems of the Chinese Ecosystem Research Network (CERN) using monitoring data collected between 2004 and 2009. The results showed that the median total N concentrations of still surface water were significantly higher in the agro- (1.5 mg·L−1) and oasis agro- ecosystems (1.8 mg·L−1) than in the forest ecosystems (1.0 mg·L−1). This was also the case for flowing surface water, with total N concentrations of 2.4 mg·L−1, 1.8 mg·L−1 and 0.5 mg·L−1 for the agro-, oasis agro- and forest ecosystems, respectively. In addition, more than 50% of the samples in agro- and oasis agro- ecosystems were seriously polluted (>1.0 mg·L−1) by N. Spatial analysis showed that the total N concentrations in northern and northwestern regions were higher than those in the southern region for both still and flowing surface waters under agro- and oasis agro- ecosystems, with more than 50% of samples exceeding 1.0 mg·L−1 (the Class III limit of the Chinese National Quality Standards for Surface Waters) in surface water in the northern region. Nitrogen pollution in agro- ecosystems is mainly due to fertilizer applications, while the combination of fertilizer and irrigation exacerbates nitrogen pollution in oasis agro- ecosystems.

Total phosphorus concentrations in surface water of typical agro- and forest ecosystems in China, 2004–2010

The concentrations of total phosphorus (TP) from 83 surface water sampling sites in 29 of the Chinese Ecosystem Research Network (CERN) monitored ecosystems, representing typical agro- and forest ecosystems, were assessed using monitoring data collected between 2004 and 2010 from still and flowing surface water. Results showed that, TP concentrations were significantly higher in agro-ecosystems than those in forest ecosystems both for still and flowing surface water. For agroecosystems, TP concentrations in the southern area were significantly higher than those in the northern and northwestern areas for both still and flowing surface water, however no distinct spatial pattern was observed for forest ecosystems. In general, the median values of TP within agro- and forest ecosystems did not exceed the Class V guideline for still (0.2 mg·L−1) or flowing (0.4 mg·L−1) surface water, however, surface water at some agroecosystem sampling sites was frequently polluted by TP. Elevated concentrations were mainly found in still surface water at the Changshu, Fukang, Linze and Naiman monitored ecosystems, where exceedance (>0.2 mg·L−1) frequencies varied from 43% to 78%. For flowing water, elevated TP concentrations were found at the Hailun, Changshu and Shapotou monitored ecosystems, where exceedance (>0.4 mg·L−1) frequencies varied from 29% to 100%. Irrational fertilization, frequent irrigation and livestock manure input might be the main contributors of high TP concentrations in these areas, and reduced fertilizer applications, improvements in irrigation practices and centralized treatment of animal waste are necessary to control P loss in these TP vulnerable zones.

A simplified method to separate latent and sensible heat fluxes using remotely sensed data

In this paper, the relationships between NDVI (normalized difference vegetation index) and pseudo thermal inertia (land surface temperature difference between day and night AVHRR data) are discussed. A simplified method was established to separate the latent and sensible heat fluxes on vegetation covered land surface. Analogous correlations between surface reflectance and LST (Land Surface Temperature) had been illustrated by several scientists who are concerned about regional estimation of soil evaporation in and or semi-arid areas. It proves work well in retrieving of soil evaporation or even aerodynamic resistance of beat transfer. The scattergram of pseudo thermal inertia versus NDVI demonstrates that higher frequency points clearly form a triangle shape, that is to say, the higher frequency points are within the triangle. The upper side of the triangle can be written as: DT/sub u/(NDVI)=a/sub u/+b/sub u/*NDVI. Similarly, the lower side of it can be denoted as: DT/sub l/(NDVI)=a/sub l/+b/sub l/*NDVI. Then, Bowen ratio B/sub i/ can be expressed as following: B/sub i/=(DT/sub u/(NDVI/sub i/)-DT/sub i/)/(DT/sub u/(NDVI/sub i/)-DT/sub l/(NDVI/sub i/))-1, where DT/sub i/ is the land surface temperature difference between day and night of the ith pixel, NDVI/sub i/ is as well. The soil heat flux G is determined empirically. After separating Rn (net radiation) into Rn/sub s/ and Rn/sub v/ (net radiation for soil and vegetation respectively) based on the vegetation fraction, the G can be obtained by: G=0.35* Rn/sub s/+0.05* Rn/sub v/, where the constant parameters may vary according to different land cover and land use.

A new algorithm to automatically determine the boundary of the scatter plot in the triangle method for evapotranspiration retrieval

Three different algorithms were developed in this paper to automatically determine the boundary of the triangle shape in the scatter plots. Experiment shows that the Algorithm III has the best performance among them based on the evaluation criteria of their robustness and computation time. The new algorithm proved to be effective to maintain the self-consistency and avoid the subjectivity in the traditional triangle method.

New instrument for determination of directional emissivity and distribution principle of directional emissivity of some major types of ground objects

As one of the three factors for multiangular remote sensing, directionality of the emissivity has an important effect on measurements. This paper puts forward one method to measure the directional emissivity of objects. According to this method, one new instrument is developed. The instrument then is applied to measure some types of ground objects and samples. This paper first describes the method and discusses several questions during the measuring process. Data of ground objects and samples are processed and analyzed. Finally, curves of directional emissivity are given.

A new measuring technique for thermal inertia of soil

To calculate thermal inertia value of soil, there must be heat-input item in to soil surface. Solar radiation on the soil surface is not shaded and is shaded using an automatic swinging plate, at the same time. The surface temperatures of not shading and shading are measured by thermal radiometer connecting to automatically the data-logging device. According to the measurements and a model the authors can calculate the soil thermal inertia. The fast measuring method for soil thermal inertia was validated by experiments that carried out at Yucheng Experimental Remote Sensing Site of Chinese Academy of Sciences. In the experiments irrigating different volume of water made the soil targets with different thermal inertia values. Stable and reasonable thermal inertia values of soil were obtained by the data that use the new method.

Retrieval of directional fraction of vegetation cover using digital camera

A simple and feasible method to retrieve directional fraction of vegetation cover is presented. A digital camera is adopted to capture multi-angle images for a wheat field and trees. The viewing angles are controlled by an automatic multi-angle observation device. After image processing, directional fraction cover and gap probability can be obtained.

Principle and practice to separate mixed surface temperature using two-temporal phases radiometric temperature

A key point is to separate mixed temperature into soil and crop surface temperatures for inverting transpiration and CO/sub 2/ fluxes. We here present a new way of using two-temporal phase information to separate mixed surface temperature in instead of tow-angle data. Soil and canopy surface radiometric temperatures are very close at the time when net radiation is equal to zero. We can summarize that the radiometric temperature difference between soil and mixed pixels are equal to the diurnal amplitude difference between the radiometric temperature of soil and canopy divided by the percent vegetation cover. In practice, the relationship between the diurnal amplitude of the radiometric temperature of the soil and mixed pixels can be found by experiments. Through simultaneous thermal infrared images with high spatial resolution we can also find out the radiometric temperature of the bare soil in mixed pixels as well as its diurnal amplitude for lower resolution images. The method was validated in the experiment of monitoring radiometric temperature of a wheat field in spring of 2000. We also found out this rule by thermal camera in the Shunyi and Yucheng experiments in 2001. Thus this method is feasible based on theory and experiments.

A new algorithm for inverting CO/sub 2/ assimilation flux

In order to understand the reasons for uncertainty in the regional estimation of carbon balances, the distributions for CO/sub 2/ assimilation in the regional scale are very useful. An algorithm for inverting the CO/sub 2/ assimilation flux is presented in this paper. The algorithm includes several improvements. First, the temperature difference model is discussed, which is used for separating the ground surface temperature using two time-phase NOAA-AVHRR data and the heat balance and thermal inertia principles instead of the two angular methods. Second an important improvement is the consideration of emissivities and downwelling atmosphere irradiances in the inverting territorial surface temperature for the algorithm.. Third, air temperature is interpolated based on ground surface temperature and wind speed also was interpolated based on surface roughness. Finally, according to the distribution image of CO/sub 2/ assimilation for wheat in North China those improvements are validated and discussed.

Thermal inertia character in Tengeli Desert of west China and seeking source of dusty storm using remote sensing data

According to measurements in 2000, thermal inertia inverted by remote sensing data can judge both soil moisture and soil particle size association. Thermal inertia and its differential is one of the judging indices for causing dusty storms. Therefore soil moisture and soil particle size are major factors for causing dusty storms. We show that the Tengeli Desert seems not to be major source of dusty storms in west-north China.