Determinants of the interannual relationships between remote sensed photosynthetic activity and rainfall in tropical Africa

The response of photosynthetic activity to interannual rainfall variations in Africa South of the Sahara is examined using 20 years (1981-2000) of Normalised Difference Vegetation Index (NDVI) AVHRR data. Linear correlations and regressions were computed between annual NDVI and annual rainfall at a 0.5° latitude/longitude resolution, based on two gridded precipitation datasets (Climate Prediction Center Merged Analysis of Precipitation [CMAP] and Climatic Research Unit [CRU]). The spatial patterns were then examined to detect how they relate to the mean annual rainfall amounts, land-cover types as from the Global Land Cover 2000 data set, soil properties and soil types. Yearly means were computed starting from the beginning of the vegetative year (first month after the minimum of the NDVI mean regime), with a one-month lead for rainfall.One third of tropical Africa displays significant (95% c.l.) correlations between interannual NDVI variations and those of rainfall. At continental scale, soil types and soil properties are only minor factors in the overall distribution of the correlations. Mean annual rainfall amounts and land-cover types are much more discriminating. The largest correlations, mostly over 0.60, are distinctly found in semi-arid (200-600 mm annual rainfall) open grassland and cropland areas. The presence of one of these two determinants (semi-aridity, and favourable land-cover type, i.e. open grassland and cropland) in the absence of the other does not systematically result in a significant correlation between rainfall and NDVI. By contrast, NDVI variations are independent from those of rainfall in markedly arid environments and in most forest and woodland areas. This results from a low signal-to-noise ratio in the former, and the fact that precipitation is generally not a limiting factor in the latter.The marginal response of NDVI to a given increase/decrease in rainfall, as described by the slope of the regression, displays a similar pattern to that of the correlation, with maximum slopes in semi-arid regions, except that a weaker response is noted in more densely populated areas, suggesting an incidence of particular land-use and agricultural practises.One-year lag relationships between annual rainfall and NDVI in the next year were also considered. Ten percent of the grid-points show significant correlations, but the spatial patterns remain difficult to interpret.     

Remote estimation of vine canopy density in vertically shoot-positioned vineyards: determining optimal vegetation indices

Three spectral vegetation indices were examined for their correlation with vertically shoot-positioned canopy density (leaf area per metre of canopy) using both field spectroscopy data at the vine scale, and aerial image analysis at the vineyard scale. Vine canopy density accounted for a significant amount of the variability in all three vegetation indices (r²= 0.65 to 0.92). The perpendicular vegetation index (PVI) was found to have the greatest information cost as well as the poorest coefficient of determination value, and thus was the least desirable of the indices examined. The ratio-based indices (RVI and NDVI) were shown to have similar information contents; however, the RVI was found to be more linearly related to canopy density over a broad range of values, and thus more desirable for vineyard remote sensing applications. Results from this analysis corroborate with findings from investigators in woodland and forest environments, and provide evidence of the complex nature of vineyard scene reflectance properties.     

基于近地光谱探测技术的冬小麦变量施肥

首先利用GreenSeeker RT200变量施肥机器系统按小区测量了田间试验区冬小麦在拔节期的归一化植被指数NDVI,然后根据改进的氮肥优化算法,由测得的NDVI数据和预测的谷物可能产量等参数,计算出氮肥需要量FNR,进而根据不同小区的氮肥需要量进行了田间变量施肥。试验结果表明,采用变量施肥之后,冬小麦的NDVI空间变异明显变小,作物长势趋于平衡。对比常规管理区和精准管理区的产量分布,精准管理区的产量不仅空间变异小,而且产量明显提高。     

Mapping tropical dry forest height, foliage height profiles and disturbance type and age with a time series of cloud-cleared Landsat and ALI image mosaics to characterize avian habitat

Remote sensing of forest vertical structure is possible with lidar data, but lidar is not widely available. Here we map tropical dry forest height (RMSE = 0.9 m, R² = 0.84, range 0.6-7 m), and we map foliage height profiles, with a time series of Landsat and Advanced Land Imager (ALI) imagery on the island of Eleuthera, The Bahamas, substituting time for vertical canopy space. We also simultaneously map forest disturbance type and age. We map these variables in the context of avian habitat studies, particularly for wintering habitat of an endangered Nearctic-Neotropical migrant bird, the Kirtland's Warbler (Dendroica kirtlandii). We also illustrate relationships between forest vertical structure, disturbance type and counts of forage species important to the Kirtland's Warbler. The ALI imagery and the Landsat time series are both critical to the result for forest height, which the strong relationship of forest height with disturbance type and age facilitates. Also unique to this study is that seven of the eight image time steps are cloud-cleared images: mosaics of the clear parts of several cloudy scenes. We created each cloud-cleared image, including a virtually seamless ALI image mosaic, with regression tree normalization. We also illustrate how viewing time series imagery as red-green-blue composites of tasseled cap wetness (RGB wetness composites) aids reference data collection for classifying tropical forest disturbance type and age. Our results strongly support current Landsat Program production of co-registered imagery, and they emphasize the value of seamless time series of cloud-cleared imagery.     

气候和人类活动对辽宁省植被变化的影响

基于2000—2019年MODIS-NDVI和气温、降水等气象数据及大气环流指数等资料,运用趋势分析、相关分析、通径分析和残差分析等方法对气候和人类活动影响下辽宁省植被动态演变特征进行探讨,并结合趋势系数和Hurst指数的叠加分析植被未来变化趋势。结果表明:辽宁省年均NDVI以0.004/a的速率增长,总体植被状况良好;空间上辽宁省植被覆盖程度主要以改善为主,辽阳市与沈阳市一带有轻微退化现象;辽宁省植被对降水的响应高于气温,2000—2019年人类活动对辽宁省植被的影响由消极转变为积极;辽宁省NDVI在反持续变化中,退化面积占到总面积的5524%,表现为分散于整个区域的空间分布状况,未来更应继续加强植被保育和退耕还林力度。     

1999-2015年长江流域上游植被覆盖特征及其对气候和地形的响应

基于SPOT NDVI指数、气象数据和数字高程模型,采用趋势分析法对1999—2015年长江流域上游地区植被覆盖空间格局和动态变化特征进行分析;利用偏相关系数法基于单个像元从动态角度研究植被覆盖对气候变化的响应;引入格网法从静态角度研究植被覆盖对气候和地形因子在整体空间格局上的响应。结果表明:研究区的植被覆盖整体较好,高覆盖地区占66.14%,表现出东高西低的梯度分布特征;从动态角度考虑,植被覆盖对温度和降水变化的响应具有较强的空间异质性,不同地区植被覆盖对温度和降水变化的动态响应关系不同;从静态角度考虑,植被覆盖对温度、降水、高程和坡度的响应表现出显著的非线性关系,存在一定的响应阈值,且都具有西部地区响应明显、东部地区响应不明显的特征。研究结果将为制定适应气候和地形的综合植被管理和土地资源管理提供科学依据。     

Do adaptive cycles of floodplain vegetation response to inundation differ among vegetation communities?

Flooding is a key driver of floodplain vegetation productivity. Adaptive cycles provide a model for examining the productivity of floodplain vegetation communities in response to hydrology. Accordingly, floodplain inundation drives vegetation productivity responses through an adaptive cycle of wetting (exploitation phase), wet (conservation phase), drying (release phase), and dry (reorganization phase). We examined changes in the productivity of four floodplain vegetation communities (lignum, coolibah, grass, and poplar box) through the four phases of an adaptive cycle and explore the various strategies used by these vegetation communities to cope with variation in water availability. All four vegetation communities showed significant differences in productivity, as indicated by changes in the normalized difference vegetation index between the adaptive cycle phases. Differences were evident in the total area of vegetation that showed a productivity response, the quality or the vigour of the response, the trajectory of change overtime (i.e., towards higher or lower productivity), and the probability of change. Although the four vegetation communities exhibited response patterns in relation to flooding and drying that fit the adaptive cycle model, differences were evident in the timing of transitions between the four phases and the duration spent in those phases for each vegetation community. Poplar box and coolibah communities showed a higher productivity response during the drying or release phase. By comparison, the highest productivity response for the grassland and lignum shrubland was observed during the wetting or exploitation phase. Overall, the results showed that the four vegetation communities are sensitive to the degree of wetting at different phases in the adaptive cycle. Knowledge of floodplain vegetation response in each phase of an adaptive cycle will enable better management of floodplains, as management activities can be tailored to adaptive phase patterns associated with each community.     

公园绿化覆盖率对人群情感恢复的影响研究

公园绿化覆盖率对人群情感恢复起到重要影响作用,但关于情感恢复的具体结果及效果的细化研究较为匮乏.选取重庆市沙坪公园中的6处空间为研究样本,以归一化植被指数(NDVI)区分空间绿化覆盖率,结合生态瞬时评估(EMA)以精确测度人群情感的恢复结果,并分析两者之间的关系,结果表明:1)以硬质铺地为主、绿化覆盖率相对较低(0.3...