Winter cover crops in Dutch maize fields: Variability in quality and its drivers assessed from multi-temporal Sentinel-2 imagery

Planting a cover crop between the main cropping seasons is an agricultural management measure with multiple potential benefits for sustainable food production. In the maize production system of the Netherlands, an effective establishment of a winter cover crop is important for reducing nitrogen leaching to groundwater. Cover crop establishment after maize cultivation is obliged by law for sandy soils and consequently implemented on nearly all maize fields, but the winter-time vegetative ground cover varies significantly between fields. The objectives of this study are to assess the variability in winter vegetative cover and evaluate to what extent this variability can be explained by the timing of cover crop establishment and weather conditions in two growing seasons (2017–2018). We used Sentinel-2 satellite imagery to construct NDVI time series for fields known to be cultivated with maize within the province of Overijssel. We fitted piecewise logistic functions to the time series in order to estimate cover crop sowing date and retrieve the fitted NDVI value for 1 December (NDVI_Dec). We used NDVI_Dec to represent the quality of cover crop establishment at the start of the winter season. The Sentinel-2 estimated sowing dates compared reasonably with ground reference data for eight fields (RMSE = 6.6 days). The two analysed years differed considerably, with 2018 being much drier and warmer during summer. This drought resulted in an earlier estimated cover crop sowing date (on average 19 days) and an NDVI_Dec value that was 0.2 higher than in 2017. Combining both years and all fields, we found that Sentinel-2 retrieved sowing dates could explain 55% of the NDVI_Dec variability. This corresponded to a positive relationship (R² = 0.50) between NDVI_Dec and the cumulative growing degree days (GDD) between sowing date and 1 December until reaching 400 GDD. Based on cumulative GDD derived from two weather stations within Overijssel, we found that on average for the past three decades a sowing date of 19 September (± 7 days) allowed to attain these 400 GDD; this provides support for the current legislation that states that from 2019 onwards a cover crop should be sown before 1 October. To meet this deadline, while simultaneously ascertaining a harvest-ready main crop, in practice implies that undersowing of the cover crop during spring will gain importance. Our results show that Sentinel-2 NDVI time series can assess the effectiveness and timing of cover crop growth for small agricultural fields, and as such has potential to inform regulatory frameworks as well as farmers with actionable information that may help to reduce nitrogen leaching.     

新冠病毒疫情期间复工复产卫星遥感监测

本文利用美国新一代极轨卫星NPP搭载的VIIRS载荷数据反演获得的热点数据,以及美国NASA的Aura卫星搭载的OMI载荷的二氧化氮对流层柱浓度资料,对中国地区2020-01—02及2019年同期,以及抗击疫情期间和后期复工复产的情况进行监测。监测结果表明：（1）2020-02较1月份及2019年同期相比,工业企业的耗能水平却出现显著降低,NO₂浓度呈现显著下降趋势。（2）全国工业热源点数和分布范围及密度自2020-02-03正式复工后稳步提升。湖北省除武汉、黄石和鄂州地区仍可监测到少数热点外,其他地区2月份均未再监测到任何热点,也证明了湖北基本没有复工迹象。（3）疫情得到基本控制之后,京津冀地区工业热源点有显著增加,但新增区域一般仍处于低能耗水平。从全国大气NO₂柱浓度监测来看,复工开始前后与2019年同期相比,污染物浓度均呈现明显下降趋势,说明复工强度有限。（4）到3月初工业热源点及其能耗水平出现显著升高,中国大部分地区的热源企业虽已逐步复工生产,说明工业产能较2月有显著提升,但生产规模或产能并未完全恢复。     

基于二三维一体化的智慧警务地理信息平台建设与研究

"智慧警务"是"智慧城市"的重要组成部分,也是社会治安防控体系发展的必然趋势,应提高认识,积极探索和论证建设"智慧警务"的模式和方法。本文阐述了基于二三维一体化的智慧警务地理信息平台建设内容和总体框架,并详细地介绍了警用地理信息系统及智慧警务应用系统建设内容和技术路线。     

卫星测高数据监测青藏高原湖泊2010年—2018年水位变化

青藏高原湖泊水位变化是气候变化和生态环境变化研究的重要指标。随着Cryosat-2观测数据的日益丰富和处理技术的提升,可以有效监测更多湖泊的水位变化信息。本研究构建了基于噪声去除技术、改进的波形重跟踪处理算法（ImpMWaPP）和误差混合动态模型为一体的高精度湖泊水位序列提取方法,利用Cryosat-2 SARIn数据获取到133个青藏高原湖泊2010年—2018年的高精度水位序列,并分析了这些湖泊水位变化的时空变化特征。总体上,青藏高原湖泊的水位继续呈上升趋势,但上升速度较2003年—2009年趋缓,年均变化率0.159 m/a。从地域分布上,北部湖泊的水位上升最为显著,而南部湖泊的水位则趋于稳定。从时间上,2010年—2012年和2016年—2018年,大多数湖泊的水位呈现快速上涨,而其他时间水位相对稳定或略有下降。     

O2-O2云反演算法及其在TROPOMI上的应用

利用遥感技术对大气环境污染进行监测时,云是影响痕量气体反演精度的重要因素,因此在痕量气体反演中需要对云的影响进行校正,通常使用的云参数主要是有效云量和云压。本文基于O₂-O₂ 477 nm吸收波段构建了O₂-O₂云反演算法：首先,根据有效云量和云高与连续反射率和O₂-O₂斜柱浓度之间的对应关系,结合假定的云模型利用VLIDORT辐射传输模型建立关于有效云量和云压的查找表;然后,通过差分吸收光谱技术拟合卫星载荷观测的大气层顶辐射,获得O₂-O₂斜柱浓度并计算连续反射率;最后,结合辅助数据,根据查找表进行插值反演获得有效云量和云压。通过将算法应用到OMI观测数据,将反演结果与OMCLDO2产品进行对比验证,有效云量和云压空间分布一致,相关系数R均超过0.97;并还将该算法应用于下一代大气成分监测仪器TROPOMI,与FRESCO+产品对比,有效云量和云压空间分布基本一致,当地表类型为海洋时,有效云量相关系数R大于0.97,云压相关系数R大于0.94,云压反演结果存在一定的区别;通过将O₂-O₂云反演算法和FRESCO+云压反演结果与CALIOP Cloud Layer产品进行对比,结果表明,在低云情况下,O₂-O₂云反演算法线性回归方程斜率为0.782,截距为198.0 hPa,相关系数R为0.850,算法表现优于FRESCO+。而在高云情况下,FRESCO+反演结果更接近CALIOP云压结果。在OMI和TROPOMI上的应用表明O₂-O₂云反演算法在大气云反演中具有较高的准确性和可行性,可以为大气痕量气体反演的校正提供云参数,并为中国同类型卫星载荷的云反演算法提供算法参考。     

羧乙基壳聚糖蒙脱石吸附养殖水体中Cu2+的应用

为了寻求性能良好、环保吸附剂,用于去除养殖水体中重金属Cu~(2+),作者利用蒙脱石负载羧乙基壳聚糖制备成复合吸附剂,并利用IR、SEM、XRD等手段分析其表面性能,将其用于处理Cu~(2+)溶液,考察了环境因子对其吸附性能的影响,并从吸附动力学和吸附热力学角度分析吸附剂对Cu~(2+)的吸附机理,最后考察其再生利用效果。结果表明:羧乙基壳聚糖成功进入到蒙脱石层间;在羧乙基壳聚糖与蒙脱石质量比为1︰25、40℃恒温水浴搅拌60min、pH=6.0、最佳投加量为4.0g/L、处理浓度不超过30 mg/L Cu~(2+)溶液时,复合吸附剂对Cu~(2+)去除率可以达到96.23%,将其用于淡水养殖鱼塘水体中, Cu~(2+)去除后可达到《渔业水质标准》规定;吸附剂对Cu~(2+)吸附热力学实验结果表明,符合Langmuir模型,反应过程为自发、吸热反应;吸附动力学结果表明该吸附符合准二级动力学方程,反应属于化学吸附;再生实验中NaOH的再生效果优于HCl。     

深水源—汇系统对多尺度气候变化的过程响应与反馈机制

源—汇系统对多尺度气候变化的响应与反馈是当前深水沉积学研究的前缘和新动向.通过梳理外陆架—深水盆地沉积物搬运分散系统(深水源—汇系统)对从构造尺度到人类尺度气候变化的过程响应,揭示了两种(迟滞和瞬态)深水源—汇系统的过程响应与反馈机制.迟滞响应深水源—汇系统的过渡区较宽、响应尺度较大(Teq≥104年),有利形成条件为...     

近六百年来长江三角洲地区城镇空间与城镇体系格局演变分析

基于历史文献、古地图和现代遥感数据,引入历史学古代城镇形态复原方法,复原（提取）明代以来长江三角洲地区113座城镇7个时间断面（1461年、1820年、1930年、1970年、1980年、2000年和2010年）下的城镇边界,采用扩张速率、扩张效率、首位度指数和位序-规模法则,分析了近六百年来区域城镇空间与城镇体系等级规模演变格局。取得以下研究结果：\mathrm{①}研究时段内,区内城镇用地总规模由205.98 km²增加到6442.19 km²,扩大了31.27倍;城镇扩张经历了萌芽阶段（明清时期）、起步阶段（民国至改革开放前夕）、成长阶段（改革开放至2000年）和加速阶段（2000—2010年）,城镇扩张速率不断加快,但扩张效率有待提升;\mathrm{②}在城镇等级规模空间格局上,明清时期南京与苏州为区内的一级城镇,民国后,上海逐渐取代其地位,从五级城镇发展成为区域核心城镇,四级以上城镇主要集中在长江干流沿岸和太湖流域,五级以下城镇大多集中在安徽;城镇体系呈首位型分布,城镇首位度较高,且改革开放后的城镇首位度较明清与民国时期要高,不同等级规模城镇之间差距扩大,大城镇优势较强。近30年,长江沿岸城镇发展加速,苏锡常都市圈、南京都市圈等逐渐形成并快速发展。     

Verification and recalibration of HY-2A microwave radiometer brightness temperature

HY-2A is the first one of the Chinese HY-2 ocean satellite series carrying a microwave radiometer(RM)to measure sea surface temperature,sea surface wind speed,atmospheric water vapor,cloud liquid water content,and rain rate.We verified the RM level 1B brightness temperature(T B)to retrieve environmental parameters.In the verification,TB that simulated using the ocean-atmosphere radiative transfer model(RTM)was used as a reference.The total bias and total standard deviation(SD)of the RM level 1B TB,with reference to the RTM simulation,ranged-20.6-4.38 K and 0.7-2.93 K,respectively.We found that both the total bias and the total SD depend on the frequency and polarization,although the values for ascending and descending passes are different.In addition,substantial seasonal variation of the bias was found at all channels.The verification results indicate the RM has some problems regarding calibration,e.g.,correction of antenna spillover and antenna physical emission,especially for the 18.7-GHz channel.Based on error analyses,a statistical recalibration algorithm was designed and recalibration was performed for the RM level 1B TB.Validation of the recalibrated TB indicated that the quality of the recalibrated RM level 1B TB was improved significantly.The bias of the recalibrated T B at all channels was reduced to<0.4 K,seasonal variation was almost eradicated,and SD was diminished(i.e.,the SD of the 18.7-GHz channel was reduced by more than 0.5K).