Performance evaluation of HY-2 series satellites in marine gravity field recovery

China has successfully launched four Haiyang-2(HY-2)series altimetry satellites.HY-2A has attracted significant attention in gravity field recovery,but the performance of other HY-2 series satellites,including HY-2B/C/D,is seldom discussed.This study evaluated the performance of all the HY-2 series satellites in recovering marine gravity field.First,the crossover discrepancies in sea surface height of the four satellites,HY-2A,HY-2B,HY-2C,and HY-2D,were analyzed to assess their altimetry stability.It was found that HY-2B had the best altimetry quality,followed by HY-2D.Subsequently,different combina-tions of altimetry data were used to calculate vertical deflections and gravity anomalies in the South China Sea(112°E-119°E,12°N-20°N).The results showed that combining data from HY-2B,HY-2C,and HY-2D improved the inversion accuracy of gravity anomalies by 0.3 mGal compared to using HY-2A data alone.HY-2C and HY-2D contributed to enhancing the accuracy of the east component of vertical deflections.

Three-dimensional thermohaline structure estimation derived from HY-2 satellite data over the Maritime Silk Road and its applications

Estimated ocean subsurface fields derived from satellite observations provide potential data sources for operational marine environmental monitoring and prediction systems.This study employs a statistic regression reconstruction method,in combination with domestic autonomous sea surface height and sea surface temperature observations from the Haiyang-2(HY-2)satellite fusion data,to establish an operational quasi-realtime three-dimensional(3D)temperature and salinity products over the Maritime Silk Road.These products feature a daily temporal resolution and a spatial resolution of 0.25°×0.25°and exhibit stability and continuity.We have demonstrated the accuracy of the reconstructed thermohaline fields in capturing the 3D thermohaline variations through comprehensive statistical evaluations,after comparing them against Argo observations and ocean analysis data from 2022.The results illustrate that the reconstructed fields effectively represent seasonal variations in oceanic subsurface structures,along with structural changes resulting from mesoscale processes,and the upper ocean’s responses to tropical cyclones.Furthermore,the incorporation of HY-2 satellite observations notably enhances the accuracy of temperature and salinity reconstructions in the Northwest Pacific Ocean and marginally improves salinity reconstruction accuracy in the North Indian Ocean when compared to the World Ocean Atlas 2018 monthly climatology thermohaline fields.As a result,the reconstructed product holds promise for providing quasi-real-time 3D temperature and salinity field information to facilitate fast decisionmaking during emergencies,and also offers foundational thermohaline fields for operational ocean reanalysis and forecasting systems.These contributions enhance the safety and stability of ocean subsurface activities and navigation.

Retrieval of Antarctic sea ice freeboard and thickness from HY-2B satellite altimeter data

Antarctic sea ice is an important part of the Earth’s atmospheric system,and satellite remote sensing is an important technology for observing Antarctic sea ice.Whether Chinese Haiyang-2B(HY-2B)satellite altimeter data could be used to estimate sea ice freeboard and provide alternative Antarctic sea ice thickness information with a high precision and long time series,as other radar altimetry satellites can,needs further investigation.This paper proposed an algorithm to discriminate leads and then retrieve sea ice freeboard and thickness from HY-2B radar altimeter data.We first collected the Moderate-resolution Imaging Spectroradiometer ice surface temperature(IST)product from the National Aeronautics and Space Administration to extract leads from the Antarctic waters and verified their accuracy through Sentinel-1 Synthetic Aperture Radar images.Second,a surface classification decision tree was generated for HY-2B satellite altimeter measurements of the Antarctic waters to extract leads and calculate local sea surface heights.We then estimated the Antarctic sea ice freeboard and thickness based on local sea surface heights and the static equilibrium equation.Finally,the retrieved HY-2B Antarctic sea ice thickness was compared with the CryoSat-2 sea ice thickness and the Antarctic Sea Ice Processes and Climate(ASPeCt)ship-based observed sea ice thickness.The results indicate that our classification decision tree constructed for HY-2B satellite altimeter measurements was reasonable,and the root mean square error of the obtained sea ice thickness compared to the ship measurements was 0.62 m.The proposed sea ice thickness algorithm for the HY-2B radar satellite fills a gap in this application domain for the HY-series satellites and can be a complement to existing Antarctic sea ice thickness products;this algorithm could provide long-time-series and large-scale sea ice thickness data that contribute to research on global climate change.

Comparative investigation of microstructure and high-temperature oxidation resistance of high-velocity oxy-fuel sprayed CoNiCrAlY/nano-Al_(2)O_(3) composite coatings using satellited powders

Satellited CoNiCrAlY–Al_(2)O_(3)feedstocks with 2wt%, 4wt%, and 6wt% oxide nanoparticles and pure CoNiCrAlY powder were deposited by the high-velocity oxy fuel process on an Inconel738 superalloy substrate. The oxidation test was performed at 1050℃ for 5, 50, 100,150, 200, and 400 h. The microstructure and phase composition of powders and coatings were characterized by scanning electron microscopy and X-ray diffraction, respectively. The bonding strength of the coatings was also evaluated. The results proved that with the increase in the percentage of nanoparticles(from 2wt% to 6wt%), the amount of porosity(from 1vol% to 4.7vol%), unmelted particles, and roughness of the coatings(from 4.8 to 8.8 μm) increased, and the bonding strength decreased from 71 to 48 MPa. The thicknesses of the thermally grown oxide layer of pure and composite coatings(2wt%, 4wt%, and 6wt%) after 400 h oxidation were measured as 6.5, 5.5, 7.6, and 8.1 μm, respectively.The CoNiCrAlY–2wt% Al_(2)O_(3)coating showed the highest oxidation resistance due to the diffusion barrier effect of well-dispersed nanoparticles. The CoNiCrAlY–6wt% Al_(2)O_(3)coating had the lowest oxidation resistance due to its rough surface morphology and porous microstructure.

On simulation of precise orbit determination of HY-2 with centimeter precision based on satellite-borne GPS technique

The HY-2 satellite carrying a satellite-borne GPS receiver is the first Chinese radar altimeter satellite, whose radial orbit determination precision must reach the centimeter level. Now HY-2 is in the test phase so that the observations are not openly released. In order to study the precise orbit determination precision and procedure for HY-2 based on the satellite- borne GPS technique, the satellite-borne GPS data are simulated in this paper. The HY-2 satellite-borne GPS antenna can receive at least seven GPS satellites each epoch, which can validate the GPS receiver and antenna design. What＇s more, the precise orbit determination processing flow is given and precise orbit determination experiments are conducted using the HY-2-borne GPS data with both the reduced-dynamic method and the kinematic geometry method. With the 1 and 3 mm phase data random errors, the radial orbit determination precision can achieve the centimeter level using these two methods and the kinematic orbit accuracy is slightly lower than that of the reduced-dynamic orbit. The earth gravity field model is an important factor which seriously affects the precise orbit determination of altimeter satellites. The reduced-dynamic orbit determination experiments are made with different earth gravity field models, such as EIGEN2, EGM96, TEG4, and GEMT3. Using a large number of high precision satellite-bome GPS data, the HY-2 precise orbit determination can reach the centimeter level with commonly used earth gravity field models up to above 50 degrees and orders.

Comparison on Winter Wheat Yield Estimating Models Based on Radarsat-2 and HJ Satellite in Huaihe River Region

The establishment of crop yield estimating model based on microwave and optical satellite images can conduct the mutual verification of the accuracy of the reported crop yield and the precision of the estimating model. With Shou County and Huaiyuan County of Anhui Province as the experimental fields of winter wheat producing areas, the linear winter wheat yield estimating models were established by adopting backscattering coefficient and Normalized Difference Vegetation Index（NDVI） based on images from the synthetic aperture radar（SAR）—RDARSAT-2 and HJ satellite photographed in mid-April and early May, 2014, and then comparisons were conducted on the accuracy of the yield estimating models. The accuracies of the yield estimating models established using co-polarized（HH） and cross-polarized（HV） modes of SAR in Jiangou Town, Shou County were 68.37% and 74.01%, respectively, while the accuracies in Longkang Town, Huaiyuan County were 63.10%and 69.10%, respectively. Accuracies of yield estimating models established by HJ satellite data were 69.52% and 66.43% in Shou County and Huaiyuan County, respectively. Accuracies of winter yield estimating model based on HJ satellite data and that based on SAR were closed, and the yield difference of winter wheat in the lodging region was analyzed in detail. The model results laid the foundation and accumulated experience for the verification, parameters correction and promotion of the winter wheat yield estimating model.

基于ICESat-2多波束激光测高数据的全球海洋重力异常反演分析

卫星测高技术是获取精细海洋重力数据的重要技术手段之一。常规卫星测高反演海洋重力异常主要是利用沿轨测高数据,而跨轨数据因较长的时间间隔或者稀疏的地面轨间距往往不能用于海洋重力异常反演,进而影响了海洋重力异常模型精度的进一步改善。新型激光测高ICESat-2能够同时获得3对光束观测数据,相邻激光束的地面间距约为3 km,为结合跨轨数据改善海洋重力异常模型提供了可能。本文首先给出了集成沿轨和跨轨数据反演海洋重力异常的处理策略;然后,分别利用沿轨数据和集成的数据构建了ICESat-2全球海洋重力异常模型(IS2Gra_alo和IS2Gra_alo_acr),结果表明通过补充跨轨数据能够有效提高沿轨数据反演海洋重力异常的精度,并验证了ICESat-2测高数据反演全球海洋重力异常的可靠性。此外,本文还探讨了ICESat-2不同跨轨数据组合对海洋重力异常模型反演精度的影响,在沿轨数据的基础上集成适当距离的跨轨观测数据能够有利于改善海洋重力异常模型的精度。本文研究为后续SWOT宽刈幅测高数据和我国双星跟飞模式测高数据反演海洋重力异常模型提供了参考意义。

Evaluation of the Long-term Performance of Microwave Radiation Imager Onboard Chinese Fengyun Satellites

Accurate brightness temperature(BT)is a top priority for retrievals of atmospheric and surface parameters.Microwave Radiation Imagers(MWRIs)on Chinese Fengyun-3(FY-3)serial polar-orbiting satellites have been providing abundant BT data since 2008.Much work has been done to evaluate short-term MWRI observations,but the long-term performance of MWRIs remains unclear.In this study,operational MWRI BTs from 2012–19 were carefully examined by using simultaneous Advanced Microwave Scanning Radiometer 2(AMSR2)BTs as the reference.The BT difference between MWRI/FY3B and AMSR2 during 2012–19 increased gradually over time.As compared with MWRI/FY3B BTs over land,those of MWRI/FY3D were much closer to those of AMSR2.The ascending and descending orbit difference for MWRI/FY3D is also much smaller than that for MWRI/FY3B.These results suggested the improvement of MWRI/FY3D over MWRI/FY3B.A substantial BT difference between AMSR2 and MWRI was found over water,especially at the vertical polarization channels.A similar BT difference was found over polar water based on the simultaneous conical overpassing(SCO)method.Radiative transfer model simulations suggested that the substantial BT differences at the vertical polarization channels of MWRI and AMSR2 over water were partly contributed by their difference in the incident angle;however,the underestimation of the operational MWRI BT over water remained a very important issue.Preliminary assessment of the operational and recalibrated MWRI BT demonstrated that MWRI BTs were substantially improved after the recalibration,including the obvious underestimation of the operational MWRI BT at the vertical polarization channels over water was corrected,and the time-dependent biases were reduced.

Validation of Chinese HY-2 satellite radar altimeter significant wave height

Chinese Haiyang-2（HY-2） satellite is the first Chinese marine dynamic environment satellite. The dual-frequency （Ku and C band） radar altimeter onboard HY-2 has been working effective to provide operational significant wave height （SWH） for more than three years （October 1, 2011 to present）.We validated along-track Ku-band SWH data of HY-2 satellite against National Data Buoy Center （NDBC） in-situ measurements over a time period of three years from October 1, 2011 to September 30, 2014, the root mean square error （RMSE） and mean bias of HY-2 SWH is 0.38 m and （-0.13±0.35） m, respectively. We also did cross validation against Jason-2 altimeter SWH data, the RMSE and the mean bias is 0.36m and （-0.22±0.28） m, respectively. In order to compare the statistical results between HY-2 and Jason-2 satellite SWH data, we validated the Jason-2 satellite radar altimeter along-track Ku-band SWH data against NDBC measurements using the same method. The results demonstrate the validation method in this study is scientific and the RMSE and mean bias of Jason-2 SWH data is 0.26 m and （0.00±0.26） m, respectively. We also validated both HY-2 and Jason-2 SWH data every month, the mean bias of Jason-2 SWH data almost equaled to zero all the time, while the mean bias of HY-2 SWH data was no less than -0.31m before April 2013 and dropped to zero after that time. These results indicate that the statistical results for HY-2 altimeter SWH are reliable and HY-2 altimeter along-track SWH data were steady and of high quality in the last three years. The results also indicate that HY-2 SWH data have greatly been improved and have the same accuracy with Jason-2 SWH data after April, 2013. SWH data provided by HY-2 satellite radar altimeter are useful and acceptable for ocean operational applications.

Assessment of the initial sea surface temperature product of the scanning microwave radiometer aboard on HY-2 satellite

HY-2 satellite is the first satellite for dynamic environmental parameters measurement of China,which was launched on 16th August 2011.A scanning microwave radiometer（RM） is carried for sea surface temperature（SST）,sea surface wind speed,columnar water vapor and columnar cloud liquid water detection.In this paper,the initial SST product of RM was validated with in-situ data of National Data of Buoy Center（NDBC） mooring and Argo buoy.The validation results indicate the accuracy of RM SST is better than 1.7 C.The comparison of RM SST and WindSat SST shows the former is warmer than the latter at high sea surface wind speed and the difference between these SSTs is depend on the sea surface wind speed.Then,the relationship between the errors of RM SST and sea surface wind speed was analyzed using NDBC mooring measurements.Based on the results of assessment and errors analysis,the suggestions of taking account of the affection of sea surface wind speed and using sea surface wind speed and direction derived from the microwave scatteromter aboard on HY-2 for SST product calibration were given for retrieval algorithm improvement.

基于Sentinel-2影像东北秋季典型湖泊大气校正方法适用性评价

本文利用6S(Second Simulation of a Satellite Signal in the Solar Spectrum)、Acolite DSF(Dark spectrum fitting)、C2RCC(Case 2 Regional Coast Color)、SeaDas(SeaWiFS Data Analysis System)、Sen2Cor(Sentinel 2 Correction)、Polymer(Polynomial based algorithm applied to MERIS)和iCOR(Image correction for atmospheric effects)7种大气校正算法,结合松花湖、月亮泡、小兴凯湖实测遥感反射率数据对“哨兵-2号”(Sentinel-2)数据进行大气校正研究,验证算法性能。整体校正结果显示,相较于实测遥感反射率,上述7种大气校正算法均在可见光波段(400~800 nm)呈现不同程度的低估。除C2RCC算法外,其余6种算法校正后的遥感反射率与实测光谱曲线变化趋势基本吻合,其中Sen2Cor算法与iCOR算法性能最佳,Polymer算法性能最差;在单波段校正精度对比中,Sen2Cor和iCOR算法几乎所有波段的均方根误差和平均绝对百分比误差都低于其余5种算法。Sen2Cor算法在560 nm、665 nm和705 nm处校正精度优于其余6种算法,iCOR算法在443 nm和740 nm处有良好的表现,在490 nm处6S算法校正精度最高,拥有最低的均方根误差(0.0059 sr^(−1))和平均绝对百分比误差(21.40%)。结果表明,这7种大气校正算法均可以在一定程度上去除大气影响,增加影像的可用性,Sen2Cor算法和iCOR算法更适用于本文所研究水体或相似水体。

Ocean Observation from Haiyang Satellites: 2012–2014

During 2012 and 2014, China has two Haiyang(which means ocean in Chinese, referred to as HY) satellites operating normally in space which are HY-1B and HY-2A. HY-1B is an ocean color environment satellite which was launched in April 2007 to observe global ocean color and sea surface temperature, and HY-2A is an ocean dynamic environment satellite which was launched in August 2011 to obtain global marine dynamic environment parameters including sea surface height,significant wave height, ocean wind vectors, etc. Ocean observation data provided by HY-1B and HY-2A have been widely used by both domestic and international users in extensive areas such as ocean environment protection, ocean disaster prevention and reduction, marine environment forecast,ocean resource development and management, ocean investigations and scientific researches, etc.

A Case Study of Impact of FY-2C Satellite Data in Cloud Analysis to Improve Short-Range Precipitation Forecast

Chinese FengYun-2C(FY-2C) satellite data were combined into the Local Analysis and Prediction System(LAPS) model to obtain three-dimensional cloud parameters and rain content. These parameters analyzed by LAPS were used to initialize the Global/Regional Assimilation and Prediction System model(GRAPES) in China to predict precipitation in a rainstorm case in the country. Three prediction experiments were conducted and were used to investigate the impacts of FY-2C satellite data on cloud analysis of LAPS and on short range precipitation forecasts. In the first experiment, the initial cloud fields was zero value. In the second, the initial cloud fields were cloud liquid water, cloud ice, and rain content derived from LAPS without combining the satellite data. In the third experiment, the initial cloud fields were cloud liquid water, cloud ice, and rain content derived from LAPS including satellite data. The results indicated that the FY-2C satellite data combination in LAPS can show more realistic cloud distributions, and the model simulation for precipitation in 1–6 h had certain improvements over that when satellite data and complex cloud analysis were not applied.

Measurement analyses and evaluations of sea-level heights using the HY-2A satellite’s radar altimeter

The HY-2A satellite is China’s first independent oceanic dynamic environmental satellite,and has been operating continuously for more than six years.The satellite’s radar altimeter,which is one of the main loads on the satellite,has the ability to realize all-weather and all-day observations of global sea-surface heights,as well as significant wave heights and sea-surface wind speeds.These observed data have been widely used in marine disaster prevention and reduction,along with resource development,maritime security and other fields.In order to achieve a comprehensive understanding of the multi-year overall observational performances of the HY-2A satellite’s radar altimeter,all of the observational data of the IGDR product from October 26,2012 to August 27,2017 were selected in this study for a comprehensive evaluation.The height measurement capability of the HY-2A satellite’s radar altimeter was evaluated using self-crossover and Jason-2 crossover methods.The height discrepancies at the self-crossover point of the HY-2A satellite’s ascending and descending orbits were also calculated.It was found that for the HY-2A satellite’s radar altimeter in global waters under the restriction conditions of ascending and descending orbits,the height anomaly differences were within a range of less than 30 cm.The absolute mean error was determined to be 5.81 cm,and the height anomaly standard deviation was 7.76 cm.Under the conditions of the observational areas being limited within a scope of 60°from the Equator,it was determined that the sea-level height anomaly differences were less than 10 cm at the junction of the ascending and descending orbits,the absolute mean error was 3.95 cm.In addition,the sea-level height anomaly standard deviation was observed to be 4.76cm.Using a mutual cross method with the Jason-2 satellite,it was found that under the conditions of the observational area being within the scope of 66°from the equator,the height anomaly differences at the junction were less than 30cm,and the absolute mean error of HY-2A and Jason-2 sea level height anomaly was 5.86 cm,with a standard deviation of 7.52 cm.It was observed that,if within the sea area the sea level height anomaly difference was limited to within 10cm,then the absolute mean error and standard deviation could reach 4.19cm and 4.98cm,respectively.It was confirmed that the HY-2A satellite’s radar altimeter had successfully reached the height measurement level of similar international altimeters.Therefore,it had the ability to meet the needs of marine scientific research and ocean circulation inversions.

基于GF-1卫星遥感反演排水河沟水体溶存N_(2)O浓度模型对比研究

[目的]探究利用GF-1卫星数据反演水体溶存氧化亚氮(N_(2)O)浓度的可行性,为实现低成本、高效率的水质实时监测提供有效途径。[方法]以宁夏青铜峡灌区第1和第5排水河沟为研究对象,选取与排水河沟水体溶存N_(2)O浓度相关性高的GF-1卫星影像波段反射率和水质参数作为自变量,通过最优子集筛选法确定最优自变量组合,分别构建了多元线性回归、BP神经网络和支持向量机模型,对水体溶存N_(2)O浓度进行预测对比。[结果]水温(T)、溶解性有机碳(DOC)等是影响水体溶存N_(2)O浓度的主要因素,同时近红外(NIR)等卫星波段与水体溶存N_(2)O浓度变化趋势显著相关。当自变量包括T,NIR等7个因素时,模型预测效果最佳。在3种模型中,BP神经网络模型验证结果R^(2)为0.64,具有最高预测精度。[结论]GF-1卫星数据以及水质参数与水体溶存N_(2)O浓度存在复杂的相关性关系,且BP神经网络能够实现利用GF-1卫星数据较高精度地反演水体溶存N_(2)O浓度。

Estimation of actual carbon dioxide removal in burned forests using satellite data:A case study in South Korea

With the increasing impact of climate change,carbon emissions and removals have become major issues.Forests are major carbon pools,and forest fires are an essential part of the carbon cycle.This study introduces a model for estimating the detailed actual CO_(2)removal in burned forests using burn severity and tree survivability.Actual CO_(2)removal was estimated from empirical yield tables without using the standard carbon removal provided by the national inventory.The primary CO_(2)calculation method followed the guidelines of the International Panel on Climate Change.The burn severity was mapped using Sentinel-2 multispectral instrument data,and the survivability of each forest type was estimated according to burn severity.The survivability was applied to the pre-fire CO_(2)removal of each forest to estimate post-fire CO_(2)removal.In our case study,the burned forest area was 1,034 ha,and the CO_(2)removal before the fire was 8,615.3t/year.After the fire,removal decreased by 81.2%to 1,618.4 t/yr.In particular,the decrease in coniferous forests was high,more than 86%.The lack of survivability data on burned trees was a major limitation of our study.Systematically accumulating field monitoring data of post-fire forests will be necessary for future research and could serve as a reference for devising immediate countermeasures against forest fires.

基于GOSAT-2卫星的中国XCO_(2)时空分布特征分析

CO_(2)是主要的温室气体之一,它对全球变暖的作用很大。自工业化以来,CO_(2)浓度在全球范围内大幅增加。为实现碳减排目标,迫切需要监测大气中的CO_(2)浓度并分析其时空分布特征。随着温室气体观测卫星的发射,利用碳卫星可以大范围地观测和分析大气中的CO_(2)浓度。本研究基于GOSAT-2卫星数据,利用克里金插值技术分析了2020年6月至2021年5月中国陆地区域的CO_(2)柱浓度(XCO_(2))的时空变化特征。结果表明,全国范围内XCO_(2)的平均值从2020年的413.86 ppm增加到2021年的419.59 ppm,增加了5.73 ppm。其中,XCO_(2)的最低值和最高值分别出现在冬季和春季。进一步的分析表明,XCO_(2)在空间分布上不一致,在人口密度较高的东南部区域浓度较高,而在人口稀少的西北部较低。此外,大城市及其周边地区的XCO_(2)普遍高于其他地区,表明人为因素导致城市地区的XCO_(2)增加过快。本文的分析结果可为碳源与碳汇的研究提供重要的基础数据和参考依据。

基于卫星遥感的中国人为CO_(2)与大气污染物排放协同关系

基于多源卫星遥感数据和大气输送模型研究我国人为CO_(2)与大气污染物(NO_(2)和CO)排放协同关系以及新冠疫情管控期间污碳排放变化特征.结果表明:高人为CO_(2)排放对应高浓度的NO_(2)和CO排放,以省级行政区为单位的2018~2020年非生长季XCO_(2)异常与XNO_(2)的相关性(r=0.79)高于与XCO的相关性(r=0.61),且高人为CO_(2)排放地区燃烧排放效率更高;2020年2月(疫情管控期)我国XCO_(2)异常、XNO_(2)、XCO下降的区域范围为2019年2月(疫情同比期)面积的50%、70%和49%,2020年2月XCO_(2)异常与XNO_(2)的相关性(r=0.71,P<0.01)高于2019年2月(r=0.59,P<0.01),而XCO_(2)异常与XCO的相关性(r=0.44,P<0.01)低于2019年2月(r=0.68,P<0.01);受大气输送的影响,2020年2月京津冀受西南方向人为排放地区输送的影响高于2019年2月,而长三角受北部长距离输送的影响降低,珠三角受大气输送的影响最小.研究结果表明卫星遥感可有效用于区域污碳协同排放时空变化特征监测.

基于多时相Sentinel-2卫星影像的冬小麦面积提取

及时准确地提取冬小麦种植信息,对开展冬小麦农情遥感监测具有重要的意义.以杭州市余杭区冬小麦越冬期(2021-12-04)、扬花期(2022-04-08)和乳熟期(2022-05-03)Sentinel-2遥感影像为数据源,分别采用最大似然法、支持向量机、归一化差值植被指数(normalized difference vegetation index,NDVI)相加和相减合成运算提取冬小麦种植面积.结合冬小麦地面调查数据与实测种植面积,对不同方法的提取结果进行精度评价.结果显示,利用越冬期影像NDVI阈值将常绿植被区(茶园、林地)掩膜处理,对非常绿植被区(建筑、水体、冬小麦)扬花期与乳熟期影像NDVI值进行和值运算,是提取余杭区冬小麦种植面积的最佳方法,面积精度为91.96%,说明基于多时相遥感影像结合植被物候特征与典型地物类型,能够实现冬小麦种植面积的高精度提取.

A study of the validation of atmospheric CO_2 from satellite hyper spectral remote sensing

Three total column dry-air mole fractions of CO_2(XCO_2) products from satellite retrievals, namely SCIAMACHY, NIES-GOSAT, and ACOS-GOSAT, in the Northern Hemisphere were validated by ground data from the Total Carbon Column Observing Network(TCCON). The results showed that the satellite data have the same seasonal fluctuations as in the TCCON data, with maximum in April or May and minimum in August or September. The three products all underestimate the XCO2. The ACOS-GOSAT and the NIES-GOSAT products are roughly equivalent, and their mean standard deviations are 2.26 × 10^(-6)and 2.27 × 10^(-6)respectively. The accuracy of the SCIMACHY product is slightly lower, with a mean standard deviation of 2.91 × 10^(-6).