Biomass estimation and uncertainty analysis based on CBERS-02 CCD camera data and field measurement

The study on terrestrial ecosystem carbon cycle has been the focus of global change research and regional sustainable development research. It is well known that terrestrial ecosystem is the largest unknown area[1] in seeking the missing carbon sink[2]. Because it is allowed in the Kyoto Protocol that adding CO2 absorption by foresting and reforesting can offset greenhouse gases emission, the mechanism of carbon sequestration and thedistribution and mapping of carbon pool have been the focus …     

Cotton pixel identification with CBERS-02 CCD data based on spectral knowledge

In this paper thein-situ experiment data are collected from the Spectral Library to estimate the possible values of the primary structural parameters in each cotton growing season by statistics. Based on these values the spectra of the cotton major growing seasons were simulated and analyzed using the canopy reflectance model, SAILH. In this way we also simulated the cotton pixel spectra corresponding to CBERS-02 CCD and took them as the reference spectra for spectra fitting. Then No. 143 Regiment of No. 8 Agricultural Division of Xinjiang Production and Construction Corps (XPCC) was chosen as the study area, and two spectra fitting methods, Mahalanobis distance and spectra angle, were used to identify cotton pixel from CBERS-02 CCD image of the study area. At last we analyzed the effect of the calibration coefficients error on cotton identifying. The results showed that within 4% error the spectral angle classifier can still have a good performance.     

The primary results of quantitative ocean color retrieval in China coastal area with CBERS CCD data

Using the techniques of quantitative ocean color sensing, the in-water ocean color algorithms for sediment and chlorophyll-a retrieval are established for CBERS-02 CCD broad spectral bands based onin situ data. The remote sensing reflectance of water is derived from CCD radiance data by a clear water atmospheric correction algorithm. Then, the sediment and chlorophyll-a concentrations are retrieved from CCD image. The sediment retrieval is quite satisfactory, but the chlorophyll-a retrieval is not so good because of the broadband width and low signal-to-noise ratio of the CCD camera.     

Comparison of the influence factors on<Emphasis Type="Italic">NDVI</Emphasis> for CCD camera and WFI imager on CBERS-02

CCD and WFI are payloads in the visible light and near infrared bands on CBERS satellites and they have not been applied widely, especially WFI. This article mainly probes into the potential of these two sensors’ application in the vegetation monitoring and analyses the influences of radiometric calibration, atmosphere conditions and sun-observing geometry, etc. onNDVI obtained from these two sensors respectively. In addition it analyses the effect of the spectral response difference of red and near infrared spectral bands in CCD and WFI sensors onNDVI. Results indicate that radiometric calibration is the most important factor onNDVI, which cannot be applied to vegetation monitoring without radiometric calibration. Results also demonstrate that near surfaceNDVI is different greatly from that of TOA which change with atmosphere conditions. The study shows thatNDVI is also affected by the non-lambertian character of surface and the change of the atmospheric path with the observing geometry. AndNDVI of WFI is higher than that of CCD. They are very different because of their spectral diffirence, but they have a good linear relevant relationship.     

Cotton pixel identification with CBERS-02 CCD data based on spectral knowledge

CBERS-02 has three sensors, Charged Coupled Device (CCD), Infrared Multispectral Scanner (IRMSS) and Wide Field Imager (WFI). Similar to Landsat TM, CCD has 4 visible and near-infrared bands and one panchromatic band. The wavelength ranges are respectively 0.45-0.52 μm, 0.52-0.59 μm, 0.63-0.69 μm, 0.77-0.89 μm and 0.51 -0.73 μm. The spatial resolution is 19.5 m. CBERS-02 has three ground stations in Beijing, Guangzhou and Urumchi, which makes it cover the whole territory. …     

The primary results of quantitative ocean color retrieval in China coastal area with CBERS CCD data

The quantitative retrieval of water constituents of coastal waters is one of the hot top- ics and a hard task in the field of ocean color sensing. As the spatial and temporal varia- tions of the water constituents in coastal or inland waters (Case-II waters) are very fast, its monitoring requires high spatial and temporal resolution sensors. So far, the require- ment has not been satisfied yet. The spatial resolution of the ocean color specific sensors is much coarser than that of the land re…     

Estimating surface evapotranspiration using combined MODIS and CBERS-02 data

Spatial scale error is one of the most serious problems in the estimates of land surface heat fluxes of sensible and latent from satellite-borne data such as MODIS 1km resolution reflectance and emissive data. One of the feasible and economic ways to decrease the spatial scale error is to use high resolution land use class data together with the MODIS data. CBERS-02 data were used to produce land use class of Baiyangdian area, Hebei Province, China in the autumn of 2004. The area ratio of each class in MODIS pixel was calculated, and used to derive the heat fluxes of the mixed pixel. The results showed that the estimated heat fluxes of soil, sensible and latent have been changed remarkably after using the high resolution land class data. It could be concluded from the comparison between simulated and ground-measured fluxes as well as the theoretical analysis that high resolution land class data are useful to diminishing the scale error of heat fluxes estimated from low resolution satellite data.

     

Estimating surface evapotranspiration using combined MODIS and CBERS-02 data

Land surface evapotranspiration is one of the most important components in water cycle between earth and atmosphere, and plays a very important role in the atmosphere, hydrosphere, and biosphere of the planet. It is an urgent task to understand the evapotranspiration process over different surface types and conditions in agriculture, hydrogeology, forest, and ecology for the purpose of using water resources properly. Additionally, land surface evapotranspiration is a key parameter in the synop…     

Applying a statistical method to streamflow reduction caused by underground mining for coal in the Kuye River basin

Streamflow in the Kuye River basin has been sharply reduced by the effects of climate change and human activities. Since 1997, the intensification of coal mining has resulted in substantial reductions to streamflow alongside an ever-increasing demand for water. In this study, we present a derived statistical method, incorporating the Mann-Kendall and Pettitt method (MK-P) and the Soil and Water Assessment Tool (SWAT), and apply it to estimating the streamflow reductions caused by underground mining for coal in the Kuye River basin. The results show that underground mining is an important cause of the streamflow reductions observed since 1997, being responsible for reductions of 21.15 mm/yr (～56% of the total) during 1997–2009. The results of the SWAT simulation were assessed by several performance criteria: Nash-Suttcliffe Efficiency (N _SE), correlation coefficient (R ²), relative error (RE), P-factor and R-factor. The close match between the simulations and observed data supports the reasonability of our findings. We suggest that engineering strategies be adopted to limit streamflow loss into goafs via fractured zones in the coalfield.     

Modeling the crop transpiration using an optimality-based approach

Evapotranspiration constitutes more than 80% of the long-term water balance in Northern China. In this area, crop transpiration due to large areas of agriculture and irrigation is responsible for the majority of evapotranspiration. A model for crop transpiration is therefore essential for estimating the agricultural water consumption and understanding its feedback to the environment. However, most existing hydrological models usually calculate transpiration by relying on parameter calibration against local observations, and do not take into account crop feedback to the ambient environment. This study presents an optimality-based ecohydrology model that couples an ecological hypothesis, the photosynthetic process, stomatal movement, water balance, root water uptake and crop senescence, with the aim of predicting crop characteristics, CO₂ assimilation and water balance based only on given meteorological data. Field experiments were conducted in the Weishan Irrigation District of Northern China to evaluate performance of the model. Agreement between simulation and measurement was achieved for CO₂ assimilation, evapotranspiration and soil moisture content. The vegetation optimality was proven valid for crops and the model was applicable for both C ₃ and C ₄ plants. Due to the simple scheme of the optimality-based approach as well as its capability for modeling dynamic interactions between crops and the water cycle without prior vegetation information, this methodology is potentially useful to couple with the distributed hydrological model for application at the watershed scale.     

Study on the relative radiometric correction of CBERS satellite CCD image

China-Brazial Earth Resources Satellite (CBERS)-01 is the first remote sensing re- source satellite of data transfer type manufactured by China and Brazil, which is full of the wisdom and sweat from both countries’ aerospace communities and is regarded as a model of the cooperation between developing countries in high-tech area. CBERS-01 was launched in October of 1999 and went into normal operation after on-orbit test inMarch of 2000. This brought an end to the history that China coul…     

A triple-exposure color PIV technique for pressure reconstruction

The study developed a triple-exposure color particle image velocimetry (TE-CPIV) technique associated with pressure reconstruction, and validated its feasibility. A light source with the three primary colors of red, green, and blue (R, G, and B) is produced in a time sequence by a liquid crystal display (LCD) projector. Particle images at three different instants under the color illuminations are captured in one snapshot using a color digital single-lens reflex (SLR) camera with a complementary metal-oxide semiconductor (CMOS) sensor. A contamination correction algorithm based on a specific calibration is performed on the different color layers (R layer, G layer, and B layer) of the raw color image to reduce the contaminated intensity of each color illumination on the other two color layers. The corrected intensity generates three new color layers, from which a standard cross-correlation process in the classical PIV method is used to obtain two velocity fields. Eventually, an instantaneous pressure field is reconstructed from the two velocity fields. The feasibility of TE-CPIV was tested by two experiments with a solid body rotation flow and a cylinder wake flow. The results show acceptable accuracy and robustness of the new technique. The idea of the TE-CPIV is believed to provide a simple and effective way of estimating a pressure field with low cost and high convenience.     

Study on the relative radiometric correction of CBERS satellite CCD image

The main payload on CBERS-01/02 of China-Brazil Earth Resources Satellite (CBERS) is a push-broom CCD camera with moderate spatial and radiant resolution. Because at lab the data for calibration at satellite assembly stage were unable to be collected, and also because the onboard calibrator after launch was in a different state from imaging, the calibration of CCD image got a series of difficulties involved. In practice, two methods are used in the processing on the ground station: One is extracting calibration data by statistics from the image itself, and the other is the method of histogram match. It was proved that the latter can calibrate the image much better, because it can remove the effect of unstable response of the camera largely and also can overcome the nonlinearity of the camera basically by using Look-Up Table (LUT) calculated from histogram statistics of different temporal images. Considering the problems of CBERS-01, a lot of calibration tests were done before the launch of CBERS-02, in which a set of lab coefficients for relative calibration was formulated after the data collection by using integration-hemisphere in the stage of satellite assembly test. During the on-orbit test, it was found that the calibration result from such coefficients was not satisfying, especially there being response difference between 3 detector arrays, which was attributed to the unstable dark currents of the CCD camera. This paper comes up with a statistic method to remove such response difference. In this method the middle detector array was used as reference to find the response differences of adjacent similar features between these arrays and it was proved to have a broad adaptability.     

Density function theory study of electronic,optical and thermodynamic properties of CaN<Subscript>2</Subscript>, SrN<Subscript>2</Subscript> and BaN<Subscript>2</Subscript>

We put forward a first-principles density-functional theory about the impact of pressure on the structural and elastic properties of bulk CaN₂, SrN₂ and BaN₂. The ground state properties of three alkaline earth diazenides were obtained, and these were in good agreement with previous experimental and theoretical data. By using the quasi-harmonic Debye model, the thermodynamic properties including the debye temperature Θ _D, thermal expansion coefficient α, and grüneisen parameter γ are successfully obtained in the temperature range from 0 to 100 K and pressure range from 0 to 100 GPa, respectively. The optical properties including dielectric function ε(?), absorption coefficient α(?), reflectivity coefficient R(?), and refractive index n(?) are also calculated and analyzed.     

Water target based cross-calibration of CBERS-02 CCD camera with MODIS data

In order to make quantitative watercolor sensing with China-Brazil Earth Resources Satellite (CBERS-02) CCD camera, the MODIS data with higher accuracy is used to cross-calibrate the CCD camera over water targets. In homogeneous clear water area, two pairs of images obtained over the same area on the same day by the two sensors are selected. The top-of-atmosphere (TOA) radiances of the multispectral bands of CCD are calculated with the water and aerosol parameters from MODIS based on a water-atmosphere radiative transfer algorithm. The stripes in CCD image that caused by unequal response of the CCD array detectors are firstly removed before making the cross-calibration. The same part of CCD detectors is selected for the calibrations in the two images to eliminate the residual error of destriping and uniformity correction for the focus plane irradiance. It is shown that the calibration results from two different images are consistent. The error of this method is about 5%.     

Estimation of forest volumes by integrating Landsat TM imagery and forest inventory data

Accurate information about forest volumes is essential for forest management planning. The survey interval of the Forest Resource Inventory of China (FRIC) is too long to meet the demand for timely decision-making required for forest protection, management, and utilization. Analysis of satellite imagery provides good potential for more frequent reporting of forest parameters. In this study, we describe an application of the k-nearest neighbors (kNN) method to Landsat TM imagery for improving estimation of forest volumes. Several spectral features were tested and compared in forest volume estimations, including normalized difference vegetation index, environmental vegetation index, and the combination of the spectral features. The combined index resulted in the most accurate volume estimations. The kNN estimator and the combined index were then used in forest volume estimation. The estimation error (RMSE) of the total volume was 44.2%, much lower than those for Larix forest (the RMSE was 51.7%) and those for the Korean pine and broadleaved forests (the estimation errors were over 71.7% and 88.19%, respectively). This preliminary study demonstrates the potential of forest volume estimations with remote sensing data to provide useful information for forest management if only limited ground information is available.     

Water target based cross-calibration of CBERS-02 CCD camera with MODIS data

The CBERS-02, the second satellite of China Brazil Earth Resources Satellite series, was launched on Oct. 21, 2002. Onboard the satellite, there are three major sensors, a CCD camera, a wide field imager and an infrared multispectral scanner (http://www. cresda.com). The purpose of this paper is to calibrate the CCD camera with a methodol- ogy of cross-calibration. The spatial resolution of the multispectal bands of CCD camera is 19.5 m, the swath is about 115 km. It is capable of side…     

Optimization of equimolar reverse constant-temperature mass-diffusion process for minimum entransy dissipation

The mass entransy describes the mass-diffusion ability of the solution system, and the mass-diffusion process with the finite concentration difference always leads to the mass-entransy dissipation. This paper studies the equimolar reverse constant-temperature mass-diffusion process with Fick's law( g∝Δ(c)). The optimal concentration paths for the MED(Minimum Entransy Dissipation) are derived and compared with those for the MEG(Minimum Entropy Generation) and CCR(Constant Concentration Ratio) operations. It is indicated that the strategy of the MED is equivalent to that of the CCD(Constant Concentration Difference) of the same component; whether the MED or the MEG is selected as the optimization objective, the strategy of the CCD is much better than that of the CCR.     

Variations of the relativistic electron flux after a magnetospheric compression event

On January 21, 2015, a sharp increase of the solar wind dynamic pressure impacted the magnetosphere. The magnetopause moved inward to the region L 8 without causing a geomagnetic storm. The flux of the relativistic electrons in the outer radiation belt decreased by half during this event based on the observations of the particle radiation monitor(PRM) of the fourth of the China-Brazil Earth Resource Satellites(CBERS-4). The flux remained low for approximately 11 d; it did not recover after a small magnetic storm on January 26 but after a small magnetic storm on February 2. The loss and recovery of the relativistic electrons during this event are investigated using the PRM data, medium-and high-energy electron observations of NOAA-15 and the Van Allen Probes, medium-energy electron observations of GOES-13, and wave observations of the Van Allen Probes. This study shows that the loss of energetic electrons in this event is related to magnetospheric compression. The chorus waves accelerate the medium-energy electrons, which causes the recovery of relativistic electrons. The Van Allen Probes detected strong chorus waves in the region L =3–6 from January 21 to February 2. However, the flux of medium-energy electrons was low in the region. This implies that the long-lasting lack of recovery of the relativistic electrons after this event is due to the lack of the medium-energy"seed" electrons. The medium-energy electrons in the outer radiation belt may be a clue to predict the recovery of relativistic electrons.     

Reaction mechanism and microstructure evolution of reaction sintered <Emphasis Type="Italic">h</Emphasis>-BN

Hexagonal boron nitride ceramic (h-BN) based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N₂ occurred vigorously at temperatures ranging from 1 000 °C to 1 300 °C, which resulted in the generation of t-BN. When the temperature exceeded 1 450 °C, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.