Xinli Wang

Spectral characteristics of infrared radiation from forest fires

Field experiments with man-made fires in a forest were conducted to verify fire warning products from satellite remote sensing techniques and to select more effective channels for producing these products. Pine branches and trunks as well as other woods were burned at a designated place in a pine-dominated forest to simulate wild forest fires when a satellite was passing over the sky. Infrared spectral irradiances, visible spectrum, brightness, and temperature were measured concurrently with satellite data at the ground using a medium and near-infrared MOMEM MR154 FT-Spectroradiometer, an infrared thermal imager, and a visible and near-infrared spectroradiometer (ASD FR). The measurements showed two emission peaks in middle infrared band that corresponded exceptionally to the combustion strength. One of the spikes at 4.17 μm reflected the CO emission peak. The other peak spanned through the wavelengths of 4.34-4.76 μm, which exhibited a much stronger response to the fire than the commonly used channel 3.5-4.0 μm for fire monitoring in remote sensing. The results suggest that the wave band 4.34-4.76 μm is probably more sensitive and more effective than the common-used channel for wild fire monitoring using satellite remote sensing techniques. However, the peak of this wavelength band drifted during the burning process, which should be taken into account in channel selection. This band is suitable to determine forest fires. Further studies are needed to use it for retrieving fire strength quantitatively.

Dependence of erythemally weighted UV radiation on geographical parameters in the United States

The relationship between solar ultraviolet (UV) radiation reaching the Earths surface and geographical parameters is helpful in estimating the spatial distribution of UV radiation, which provides useful information to evaluate the potential impacts of enhanced UV levels on human health, agriculture, environment, and ecosystems for sustainable development. Measurements of erythemally weighted UV radiation at the sites of the United States Department of Agriculture UV-B Monitoring and Research Program (UVBMRP) monitoring network were analyzed to investigate the geographical distribution and seasonal variations. Twenty nine observation sites, which had continuous measurements during the recent six years, are selected for this study; twenty seven of them are distributed in the United States, including one in Hawaii and one in Alaska, and two of them are located in Canada along the United States border. The measurements were taken using the Yankee Environmental Systems Inc. (YES) UVB-1 ultraviolet pyranometer. This work focuses the data from the recent six years of 2001-2006 and the measurements during summer months (June-August) are emphasized. For each day, the measurements are integrated from sunrise to sunset to produce the daily UV dosage, which is then averaged for different seasons or for the whole year over the six years to generate the average daily UV dosage. A multivariable regression technique is exploited to characterize the dependence of UV dosages on geographical parameters, including latitude and altitude. The results show that, although there are many factors, such as clouds, ozone, aerosols, air pollutants, and haze, that affect the UV radiation intensity at a location, the latitude and altitude of the site are the primary factors that regulate the average daily UV dosage. On average over the last six years in the United States, more than 95% of the variability in averaged daily UV dosages can be explained by the latitude and altitude. Longitude is not statistically significant in predicting UV irradiance. Nonlinear relationships can be statistically established between averaged daily UV dosage and latitude and altitude. The effects of latitude on UV radiation are much more significant than the altitude. The average daily UV dosages decrease exponentially with the latitude. While an increase of one degree in latitude may lead to a decrease of more than 350 Jm-2day-1 in the averaged daily dosage in the low latitudes, the decrease is around 100 Jm-2day-1 in the mid latitudes and less than 50 Jm-2day-1 in the high latitudes. The averaged daily UV dosage increases with altitude almost linearly until up to 1500 meters. Then it increases gradually and no significant increases can be detected above 2600 meters. Although the regression against latitude and altitude is statistically highly significant, notable deviations from the regression predictions are observed in the lower and mid latitudes and lower altitudes. These discrepancies are most likely due to the intense anthropogenic activities and natural events occurring in this area, including natural fire, industrial production, driving, and farming. These locally dependent activities will generate more UV absorbers into the air.

An optimal staggered canopy system for high yield cultivation of cotton and light distribution in the canopy

Staggered canopy system is an effective planting practice for high yield by maximizing light penetration into the canopy of cotton (Gossypium hirsutum L.) plants. Compared with traditional cropping practices, this system produces higher yields in general. A staggered canopy system is constructed by planting two cultivars of different shoot architectures to form a canopy of two leaf layers. Field experiments of four treatments were carried out to determine the optimal pattern of staggered canopy. Solar radiations at different heights in the canopies were measured at a vertical interval of 20 cm between and within rows, using a digital light intensity meter. The optimal planting pattern for high yields consisted of two rows of tall plants bracketing a row of short plants with a wide spacing of 100 cm around the rows of short plants, which formed a staggered canopy. The available photosynthetic photon flux density in the staggered canopy was higher than in the canopy of conventionally planted field after the canopies were closed. The staggered canopy system allows more light penetration into the canopy than the conventional, where light was deducted sharply by an excessively dense canopy. In addition, wind speeds and CO2 concentrations inside the staggered canopy were greater than those in the conventional. The staggered canopy has an improved canopy structure compared to a conventional planting practice.

Detection and projection of climate changes in Jianghuai Valley, China

Climate changes in the past decades in Jianghuai Valley are detected systematically by using statistical techniques in this study. The results show that the feature of the climate change is warming. Both temperature and precipitation are now in the phase of a relative high climatic base state and the phase of high climatic variability. Therefore, both frequency and strength of extreme climate events such, as hot weather, droughts, and floods, have increased remarkably since 1990s. Finally, the RCM PRECIS developed by Hadley Center for Climate Prediction and Research is used to provide the predictions of future climate in the valley. The results give an average surface warming of 2.9°C under the SRES B2 emissions scenario by the end of this century (2071-2100). And the precipitation may have a lager increase.

Simulations of IPCC SRES effect upon winter wheat growing in the Chinese Huang-Huai valley

Using 1994-2006 typical-station agricultural data of the Huang-Huai winter wheat zone for the adjustment and validation of the DSSAT-CERES Wheat model, which is then used with the IPCC SRES climate scenarios (A2 and B2) through a stochastic weather generator, simulation is undertaken of effects of the 2050s climate regime on winter wheat yield, growth/development and water requirement in the Huang-Huai plain. Results suggest that of the two emission schemes, A2 gives higher negative influence compared to B2; the wheat growth/development period is shortened by 18 days, on average, for the region due to global warming leading to the accelerated growth, the flowering occurring ~20 days in advance, the span from flowering to maturity shortened 1~2 days, and the regional yield reducing by ~10%, on the average. Enough irrigation will be needed to alleviate the yield decline but the wheat productivity per unit water volume is to reduce.

Estimation of Soil Moisture of Winter Wheat Fields in Henan Province of China

In line with the equation of soil moisture balance and the results from field experiments for years, the source and consumption of soil water components and their calculating models were scientifically analyzed. And based on the wheat condition in its whole growth and development period, as well as water consumption pattern and soil water stress index, a computer-based comprehensive study was made for discussing spatial distribution of non-stress soil water content, field moisture utilization and irrigation mode for winter wheat in different climate years to provide useful suggestion as to directing irrigation and management. The analysis showed that: no matter under what type of climatic conditions, winter wheat fields need irrigation at least once in northern part of Henan Province, however, in southern part, especially the southern area of Huai River, irrigation is needless; cornfields in the middle of the province should be irrigated once in the years short of precipitation, while not be irrigated in the years with abundant rainfall.

Spatial distribution and temporal variation of ecological capital and their relation to climate change and the changes of land use and land cover on the northern slope of the Tianshan Mountain, China

Ecological capital of an ecosystem is the total value of the direct biological products in the system and the value of ecological service. The assessment of ecological capital is a new research area emerged from the challenge in the interdisciplinary research of ecology and social development. It is fundamental to establish a green national economy accounting system. Scientific evaluation of ecological capital is helpful for considering ecological cost in making the decision for economic development, and it is demanded for sustainable development. In this study, a quantitative assessment model of ecological property has been developed based on the analysis of per unit yield in the conventional ecology together with the utilization of remote sensing data from the Landsat TM, CBERS, MODIS, and NOAA database, land use and land cover data, and field measurements. The study area covers Changji Autonomous District, Xinjiang, China on the northern slope of Tianshan Mountain that is located in a typical arid area. Dynamic monitoring of ecological capital was performed using remote sensing techniques. Spatial distribution and temporal variation of ecological properties were characterized. The effects of land cover and land use as well as climate change on those variation and distribution were analyzed. The results show a significant increase in the ecological capital during 1990-2003. The spatial distribution of ecological properties is characterized by a negative gradient from higher altitudes to lower altitudes (plains) and from oases to deserts, which is consistent with the zonal distribution of vegetation in arid areas. Due to global warming, the climate in Xinjiang has been changed into a warmer and wetter environment during the last 50 years, which improves the plant growing conditions in the alpine regions, piedmont hilly regions, and the oases. On the other hand, the natural environment in the arid and semiarid regions in northwest China becomes more severe, and the stress to the natural ecosystems becomes more and more serious. Human activities affect the quality and the area of ecosystems and change the service functions of ecosystems. Consequently the fluctuation of ecological capital occurs.

Correlation analysis between the biomass of oasis ecosystem and the vegetation index at Fukang

The information of biomass and productivity of an ecosystem is an essential to evaluate the ecosystem and its environment. This sort of data is usually retrieved from satellite data. However, the accuracy of the retrieval and the algorithms for the retrieval vary with the environment and the type of the ecosystem. In this study, the relationship between the biomass of oasis ecosystems at Fukang, Xinjiang, China and the normalized vegetation index (NDVI) was established in order to derive biomass data of the ecosystem from satellite data. The NDVI data were from the MODIS data with a resolution of 250 meters. Biomass measurements were taken in August, 2003 at 53 sampling sites. Linear and nonlinear regression analyses were performed on this data set. In general, the nonlinear models perform better than the linear models although all of them can successfully generate biomass data with the input of NDVI. Among those nonlinear models, the model Y=5593.3NDVI3+7509.7NDVI2-1268.9NDVI+191 performs the best in terms of the retrieval accuracy, where Y represents the biomass.

Spectral distribution of UV-B irradiance derived by synthetic model compared with simulation results of TUV and ground measurements

Multifilter rotating shadowband radiometers are deployed in the United States, Canada, and New Zealand by the USDA (United States Department of Agriculture) UV-B (ultraviolet-B) Monitoring and Research Program to measure UV-B irradiances at seven discrete wavelengths. A synthetic model is used to construct the continuous spectral distribution, from which irradiance integrals can be performed for various purposes. The derived spectral data are posted for public use through a web accessible database. Although the synthetic model has been validated with a certain data set, few works have been seen to compare the results of the synthetic model with simulations of other widely accepted models such as TUV. Through this comparison the validation of the synthetic model can be further confirmed and alternative techniques for constructing spectral irradiances from discrete narrowband measurements can also be explored. In this study the data from the USDA UV-B Monitoring and Research Program are used to evaluate the synthetic model and to explore the capability of the TUV model for constructing continuous spectra from discrete measurements. Simulations of the TUV model are compared with discrete measurements, erythema-weighted broadband measurements, and the results of the synthetic model. Good agreements between derived results by using TUV model and the synthetic model with measurements in general further confirm the validation of the synthetic model. Generally, the spectral irradiances constructed by using synthetic model are lower than those by using the TUV model at very shorter wavelengths (<301 nm) and at the wavelengths of 315-342 nm, but are higher at other wavelengths. The ratio of erythemal doses derived by using the TUV simulation to broadband measurements varies between 0.87-1.02. Constructed erythemal doses by using the TUV simulation are closer to broadband measurements than those obtained by using the synthetic model. These results suggest that the TUV model may be a good alternative to accurately estimate continuous spectral distributions from discrete measurements.

Preliminary results of a UV-B effect incorporated GOSSYM model

Field experiments and laboratory tests have shown multiple effects of enhanced ultraviolet-B (UV-B) radiation on cotton growth, development, and yield. Adverse effects include development of chlorotic and necrotic patches on leaves, reductions in total leaf area, plant height, photosynthesis, and yield. However, little work has been carried out to incorporate these experimental results into a simulation model and to estimate the effects of UV-B radiation under field conditions with varied environments and management practices. This study incorporates experimental results of UV-B effects on cotton crop into a cotton simulation model, GOSSYM, which is being used widely in various applications. In this work, first modules were modified to incorporate the effects of UV-B radiation on canopy photosynthesis, leaf area expansion, and stem and branch elongation. Then, the modified model was used to test the validity of model assumptions and algorithms on independent experimental data sets. Finally, preliminary studies were performed to simulate the effects of UV-B radiation in the field conditions at Stoneville, Mississippi using 30-year (1964-1993) climate data. Simulation results agreed well with experimental measurements, proving the validation of the model. Our results suggest that cotton lint yield declined with increased UV-B radiation. The reductions were 20% when UV-B irradiance was 12 kJ m-2 under irrigated conditions. Similar reductions in yield were predicted at lower UV-B radiation (11 kJ m-2) under rain-fed conditions. The modified model will be useful to simulate the impacts of UV-B radiation on cotton growth and yield under current and future climatic conditions and to suggest management options to mitigate the adverse effects.