Assessment of vegetation cover changes and the contributing factors in the Al-Ahsa Oasis using Normalized Difference Vegetation Index(NDVI)

The abandonment of date palm grove of the former Al-Ahsa Oasis in the eastern region of Saudi Arabia has resulted in the conversion of delicate agricultural area into urban area.The current state of the oasis is influenced by both expansion and degradation factors.Therefore,it is important to study the spatiotemporal variation of vegetation cover for the sustainable management of oasis resources.This study used Landsat satellite images in 1987,2002,and 2021 to monitor the spatiotemporal variation of vegetation cover in the Al-Ahsa Oasis,applied multi-temporal Normalized Difference Vegetation Index(NDVI)data spanning from 1987 to 2021 to assess environmental and spatiotemporal variations that have occurred in the Al-Ahsa Oasis,and investigated the factors influencing these variation.This study reveals that there is a significant improvement in the ecological environment of the oasis during 1987–2021,with increase of NDVI values being higher than 0.10.In 2021,the highest NDVI value is generally above 0.70,while the lowest value remains largely unchanged.However,there is a remarkable increase in NDVI values between 0.20 and 0.30.The area of low NDVI values(0.00–0.20)has remained almost stable,but the region with high NDVI values(above 0.70)expands during 1987–2021.Furthermore,this study finds that in 1987–2002,the increase of vegetation cover is most notable in the northern region of the study area,whereas from 2002 to 2021,the increase of vegetation cover is mainly concentrated in the northern and southern regions of the study area.From 1987 to 2021,NDVI values exhibit the most pronounced variation,with a significant increase in the“green”zone(characterized by NDVI values exceeding 0.40),indicating a substantial enhancement in the ecological environment of the oasis.The NDVI classification is validated through 50 ground validation points in the study area,demonstrating a mean accuracy of 92.00%in the detection of vegetation cover.In general,both the user’s and producer’s accuracies of NDVI classification are extremely high in 1987,2002,and 2021.Finally,this study suggests that environmental authorities should strengthen their overall forestry project arrangements to combat sand encroachment and enhance the ecological environment of the Al-Ahsa Oasis.

基于绿视率和NDVI的城市街道景观分析与优化研究

街道景观空间对市民健康和城市风貌具有重要影响。既往研究中常以归一化植被指数(NDVI)和绿视率(GVI)来分别代表二维和三维的绿色指标,但对二者的指标相关性研究甚少。采用基于深度学习的图像语义分割方法分析百度街景计算代表性街道的GVI,利用GF-1卫星数据计算NDVI,比较分析城市街道的GVI和NDVI指标特征及相关性。结果表明,1)中山市中心城区各代表街道GVI指标参差不齐,从8.06%到36.00%,其中石岐街道兴中道GVI最高;2)各街道观测点的NDVI均值随着缓冲区尺度的增加也随之呈现出不同变化,NDVI均值具有强烈的尺度敏感性;3)50 m GVI和DNVI均值的皮尔逊相关系数最高,达到0.832。在此基础上分析街道景观存在的不足并给出优化建议,为城市街景评估、空间优化、景观提升提供参考。

Retrospective analysis of two northern California wild-land fires via Landsat five satellite imagery and Normalized Difference Vegetation Index (NDVI)

Wild-land fires are a dynamic and destructive force in natural ecosystems. In recent decades, fire disturbances have increased concerns and awareness over significant economic loss and landscape change. The focus of this research was to study two northern California wild-land fires: Butte Humboldt Complex and Butte Lightning Complex of 2008 and assessment of vegetation recovery after the fires via ground based measurements and utilization of Landsat 5 imagery and analysis software to assess landscape change. Multi-temporal and burn severity dynamics and assessment through satellite imagery were used to visually ascertain levels of landscape change, under two temporal scales. Visual interpretation indicated noticeable levels of landscape change and relevant insight into the magnitude and impact of both wild-land fires. Normalized Burn Ratio (NBR) and delta NBR (DNBR) data allowed for quantitative analysis of burn severity levels. DNBR results indicate low severity and low re-growth for Butte Humboldt Complex “burned center” subplots. In contrast, DNBR values for Butte Lightning Complex “burned center” subplots indicated low-moderate burn severity levels.

东北三省NDVI时空变化特征及对气候因子的响应

中国东北地区是全球气候变化最敏感的区域之一,了解植被的时空变化及对气候因子的响应对东北地区生态环境的构建和评价具有重要意义,对全球气候变化的响应也具有重要的指示作用。基于MODIS归一化差值植被指数(NDVI),利用Theil-Sen斜率估计、Mann-Kendall检验和Hurst指数开展2000—2021年东北三省NDVI时空演变特征及未来变化趋势研究,并通过相关分析方法研究NDVI对气候因子的响应。结果表明:2000—2021年NDVI整体均值为0.391,季节上呈现出春冬季低、夏秋季高的变化趋势,空间上呈现出西低东高的变化趋势;2000—2021年,NDVI年均增长率为0.003 a~(-1),而2010—2021年,NDVI整体呈现极显著上升趋势,年均增长率为0.006a~(-1);东北三省86.93%面积的NDVI在未来可持续增长,表明未来植被生长态势较好;相关分析表明,NDVI与气候因子在空间尺度上存在依赖性,气温与NDVI有更好的相关性;在东北三省大部分地区,气温和降水均对NDVI变化有正贡献,且两者的贡献相当,但在空间上存在着差异。

Correction to:Commentary review on the use of normalized difference vegetation index(NDVI)in the era of popular remote sensing

The article“A commentary review on the use of normalized difference vegetation index(NDVI)in the era of popular remote sensing”,written by Sha Huang·Lina Tang·Joseph P.Hupy·Yang Wang and Guofan Shao,was originally published electronically on the publisher’s internet portal on 31st May 2020 without open access.With the author(s)’decision to opt for Open Choice the copyright of the article changed on 25th July 2020 to©The Author(s)2020 and the article is forthwith distributed under a Creative Commons Attribution 4.0 International License(https://creativecommons.org/licenses/by/4.0/),which permits use,sharing,adaptation,distribution and reproduction in any medium or format,as long as you give appropriate credit to the original author(s)and the source,provide a link to the Creative Commons licence,and indicate if changes were made.

基于MODIS-NDVI数据的延河流域植被覆盖时空变化及其对极端降水的响应

基于2010-2020年MODIS-NDVI数据,分析延河流域归一化植被指数(normalizeddifference vegetation index,NDVI)和极端降水指数,辅以利用Sen趋势分析、M-K趋势检验法、Pearson相关分析等方法,研究植被覆盖时空变化及其对极端降水的响应。结果表明:1)2010-2020年,延河流域NDVI呈显著增加趋势,植被覆盖状况逐年改善,其增加速率为0.073/(10 a)(P<0.001);2)空间上,延河流域NDVI呈现从东南到西北减小的布局;3)趋势上,NDVI呈上升和减小趋势的面积占比分别为98.02%和1.98%,整体呈上升趋势,植被覆盖显著改善;4)近11年极端降水指数总体趋势变化平缓,R20(number of very heavy precipitation days)、RX_(5day)(max5-day precipitation amount)、CDD(consecutive dry Days)和CWD(consecutive wet days)呈上升趋势,R_(95P)(very wet day precipitation)和SDII(simple daily intensity index)呈下降趋势;5)NDVI与极端降水指数的相关性整体上偏低,除SDII外,其余指数都与NDVI正相关,且NDVI与RX_(5day)相关性最强,与R20相关性最弱。

基于MODIS数据的青藏高原生长季植被NDVI的时空变化分析

利用2001—2020年分辨率1 km MODIS归一化植被指数(NDVI)产品探讨青藏高原生长季植被的时空变化特征及规律。研究发现青藏高原生长季植被NDVI在空间上具有异质性,其数值从东南向西北逐渐递减,多年均值为0.14;近20 a来NDVI的稳定生长区和改善区面积达到94%,青藏高原整体呈现出变绿趋势;NDVI与海拔呈负相关关系,平均海拔每升高1000 m,NDVI下降0.09。研究结果为保护青藏高原生态系统等方面提供一定的科学参考。

黑龙江省植被生长季NDVI时空变化及气候响应分析

为了解黑龙江省植被动态变化及探究植被与气候因子之间的关系,本文基于2000—2020年植被生长季(4—10月)的MOD13Q1-NDVI数据,分析其植被空间分布、时空动态变化及变异系数CV;同时结合气候因子,分析植被归一化植被指数(NDVI)变化与气温、降水和相对湿度的响应特征。结果表明,2000—2020年该地区植被生长季NDVI多年平均值为0.57,总体呈北部和东南部高,东北部和西南部低;21年来植被生长季NDVI整体呈显著改善趋势,年变化率为0.0035(P<0.01)。植被改善区域远大于其退化区域,且以明显改善为主,仅3.35%的区域呈退化趋势;NDVI的变异系数以低波动和相对低波动为主,分布占比为38.77%和51.89%;植被NDVI与气温、降水和相对湿度均呈正相关性。气温、降水和相对湿度对植被NDVI变化的相对贡献率分别为28.00%、26.17%和45.83%;相对湿度是影响植被NDVI变化的主要气候因子。

基于NDVI和EVI不同植被指数表征的粤港澳大湾区植被空间格局驱动因子影响力比较分析

为研究归一化植被指数(normalized difference vegetation index,NDVI)和增强植被指数(enhanced vegetation index,EVI)的表征差异是否会造成有关植被研究的结果差异,分别在采用2005—2020年MODISNDVI、MODIS-EVI 2种不同遥感植被指数表征粤港澳大湾区植被空间特征的基础上,以同时期17个自然因子和人为因子作为驱动因子,通过地理探测器模型方法,计算各驱动因子对基于NDVI和EVI的植被空间特征的影响力。结果显示,虽然粤港澳大湾区南亚热带-热带植被在NDVI和EVI的表征下,其结果存在差异,但在不同植被指数下,通过地理探测器模型方法计算各驱动因子影响力量化及排序结果基本一致,未受不同植被指数表征差异的影响。在驱动因子中,土地利用类型、高程均是最主要驱动因子,对植被空间分布影响力均超过50%。因子之间均表现出双因子增强作用。土地利用类型协同人口分布因子对NDVI表征下的植被空间分布影响力最强;高程协同人口分布因子对EVI表征下的植被空间分布影响力最强。研究结果表明,虽然NDVI、EVI在表征植被覆盖特征方面存在差异,但是基于不同植被指数计算的驱动因子定量分析结果趋于一致。

1981~2020年昆仑山-阿尔金山草地NDVI时空变化及其对气温、降水的响应

基于NOAA-AVHRR NDVI数据,采用最大值合成法、回归分析法与相关分析法,探讨了1981~2020年昆仑山-阿尔金山草地归一化植被指数(NDVI)时空变化及其对气温、降水的响应。结果显示:1981~2020年,昆仑山-阿尔金山草地NDVI具有时序波动,在1989~1994年、1995~2000年与2006~2020年草地NDVI表现为显著增加。草地NDVI自西向东逐渐递减,多年均值为0.227(±0.037),相较于1981年(0.213),2020年(0.257)增加了0.044;过去40年,占昆仑山-阿尔金山草地总面积15.00%的草地NDVI呈显著增加,13.00%为显著减少。1981~2020年,昆仑山-阿尔金山气候变化以“暖湿化”(面积占比为48.02%)为主,草地NDVI与气温表现为正相关,与降水呈负相关,与气温、降水呈显著正相关的草地面积占比分别为18.00%、2.00%,呈显著负相关的面积占比分别为2.00%、11.00%。高寒草原类、温性荒漠类呈“暖湿化”的面积占比分别为18.06%、11.04%,相应的草地NDVI呈显著增加的面积占比分别为14.18%、16.82%;温性荒漠类对气温、降水呈显著正响应的面积占比分别为3.28%、0.60%;高寒草原类与气温呈显著正相关的面积占比为6.77%,与降水呈显著负相关的面积占比为4.94%。昆仑山北坡气温上升与适度的降水增加有利于草地植被生长,但降水的过度增加可能导致滑坡、泥石流,破坏草地生境,影响草地植被生长。

Interannual Variability of the Normalized Difference Vegetation Index on the Tibetan Plateau and Its Relationship with Climate Change

The Qinghai-Xizang Plateau, or Tibetan Plateau, is a sensitive region for climate change, where the manifestation of global warming is particularly noticeable. The wide climate variability in this region significantly affects the local land ecosystem and could consequently lead to notable vegetation changes. In this paper, the interannual variations of the plateau vegetation are investigated using a 21-year normalized difference vegetation index （NDVI） dataset to quantify the consequences of climate warming for the regional ecosystem and its interactions. The results show that vegetation coverage is best in the eastern and southern plateau regions and deteriorates toward the west and north. On the whole, vegetation activity demonstrates a gradual enhancement in an oscillatory manner during 1982-2002. The temporal variation also exhibits striking regional differences： an increasing trend is most apparent in the west, south, north and southeast, whereas a decreasing trend is present along the southern plateau boundary and in the central-east region. Covariance analysis between the NDVI and surface temperature/precipitation suggests that vegetation change is closely related to climate change. However, the controlling physical processes vary geographically. In the west and east, vegetation variability is found to be driven predominantly by temperature, with the impact of precipitation being of secondary importance. In the central plateau, however, temperature and precipitation factors are equally important in modulating the interannual vegetation variability.

基于K_(c)和NDVI关系的蒸散发量空间尺度提升及时空变化

为探究流域长时序高空间分辨率蒸散发量计算对区域水资源开发利用、水利工程规划设计及农业可持续发展的重要意义,以河北省邢台市柳林流域为研究对象,基于Penman-Monteith模型和蒸渗仪实测蒸散发数据计算不同时期的流域作物系数(Kc),并建立Kc与归一化植被指数(normalized difference vegetation index,NDVI)的关系,利用250 m分辨率NDVI产品将蒸渗仪测算的蒸散发量升尺度到柳林流域,计算流域各网格2000—2021年的蒸散发量,分析蒸散发量的时空变化规律。结果表明:柳林流域多年平均潜在蒸散发量为1135.6 mm,呈下降趋势;多年平均蒸散发量为591.4 mm,呈上升趋势。蒸散发量在空间上西北高东南低,四季蒸散发量空间分布特征与多年平均蒸散发量一致,且季节上分配不均。基于NDVI估算的蒸散发量与水量平衡法计算的蒸散发量2000—2020年多年平均相对误差为7.9%,说明利用Kc与NDVI关系可以较精确地对蒸散发量进行空间尺度提升。

Drought trend analysis in a semi-arid area of Iraq based on Normalized Difference Vegetation Index, Normalized Difference Water Index and Standardized Precipitation Index

Drought was a severe recurring phenomenon in Iraq over the past two decades due to climate change despite the fact that Iraq has been one of the most water-rich countries in the Middle East in the past.The Iraqi Kurdistan Region(IKR)is located in the north of Iraq,which has also suffered from extreme drought.In this study,the drought severity status in Sulaimaniyah Province,one of four provinces of the IKR,was investigated for the years from 1998 to 2017.Thus,Landsat time series dataset,including 40 images,were downloaded and used in this study.The Normalized Difference Vegetation Index(NDVI)and the Normalized Difference Water Index(NDWI)were utilized as spectral-based drought indices and the Standardized Precipitation Index(SPI)was employed as a meteorological-based drought index,to assess the drought severity and analyse the changes of vegetative cover and water bodies.The study area experienced precipitation deficiency and severe drought in 1999,2000,2008,2009,and 2012.Study findings also revealed a drop in the vegetative cover by 33.3%in the year 2000.Furthermore,the most significant shrinkage in water bodies was observed in the Lake Darbandikhan(LDK),which lost 40.5%of its total surface area in 2009.The statistical analyses revealed that precipitation was significantly positively correlated with the SPI and the surface area of the LDK(correlation coefficients of 0.92 and 0.72,respectively).The relationship between SPI and NDVI-based vegetation cover was positive but not significant.Low precipitation did not always correspond to vegetative drought;the delay of the effect of precipitation on NDVI was one year.

Simple method for extracting the seasonal signals of photochemical reflectance index and normalized difference vegetation index measured using a spectral reflectance sensor

A spectral reflectance sensor(SRS)fixed on the near-surface ground was developed to support the continuous monitoring of vegetation indices such as the normalized difference vegetation index(NDVI)and photochemical reflectance index(PRI).NDVI is useful for indicating crop growth/phenology,whereas PRI was developed for observing physiological conditions.Thus,the seasonal change patterns of NDVI and PRI are two valuable pieces of information in a crop-monitoring system.However,capturing the seasonal patterns is considered challenging because the vegetation index values estimated by the reflection from vegetation are often governed by meteorological conditions,such as solar irradiance and precipitation.Further,unlike growth/phenology,the physiological condition has diurnal changes as well as seasonal characteristics.This study proposed a novel filtering method for extracting the seasonal signals of SRS-based NDVI and PRI in paddy rice,barley,and garlic.First,the measurement accuracy of SRSs was compared with handheld spectrometers,and the R^(2)values between the two devices were 0.96 and 0.81 for NDVI and PRI,respectively.Second,the experimental study of threshold criteria with respect to meteorological variables(i.e.,insolation,cloudiness,sunshine duration,and precipitation)was conducted,and sunshine duration was the most useful one for excluding distorted values of the vegetation indices.After data processing based on sunshine duration,the R^(2)values between the measured vegetation indices and the extracted seasonal signals of vegetation indices increased by approximately 0.002–0.004(NDVI)and 0.065–0.298(PRI)on the three crops,and the seasonal signals of vegetation indices became noticeably improved.This method will contribute to an agricultural monitoring system by identifying the seasonal changes in crop growth and physiological conditions.

基于Copula函数的北京市气候变化及人类活动对NDVI影响的识别

在气候变化和人类活动的双重影响下,城市植被受到严重影响,识别气候变化和人类活动对植被的影响,对城市的生态建设具有重要意义。本文依据《北京市城市总体规划》,运用Copula函数的方法考虑气候变化和人类活动对植被的影响进行分析。结果表明:北京市的植被在各个季节都呈现出较好的增长趋势,且在生态涵养区的增长趋势更加明显。NDVI-P的最优Copula函数主要为Frank Copula和Clayton Copula,而NDVI-T的最优Copula函数主要是Frank Copula函数。根据Copula函数的依赖结构分析表明,气候变化主要是通过影响植被的生长期和促进植被的光合作用来影响植被的生长;人类活动对植被的影响主要是通过建设活动与政策来影响植被的分布。

Monitoring the Sequential Cropping Index of Arable Land in Zhejiang Province of China Using MODIS-NDVI

The sequential cropping index of arable land is important agricultural information. The aim of this article is to monitor and analyze the parameter, and offer reference for agricultural production. The cropping index of arable land in Zhejiang Province, China from 2001 to 2004 was calculated using the second order difference based MODIS （moderate resolution imagine spectroradimeter） vegetation data from NASA （National Aeronautic and Space Administration） in America and the land use map with a scale of 1：25 000. It was found that the peak of the time series of the NDVI curve indicated that the ground biomass of crops reached the maximum, and fluctuated with the crops growing processes such as sowing, seeding, heading, ripeness, and harvesting within one year. Thus, the sequential cropping index was defined as the number of peaks of the time series of the NDVI curve. The sequential cropping index of all cities in Zhejiang Province, China was worked out. It is seen from the spatial distribution that the cropping index in the southwest Zhejiang Province is larger than that in the northeast. As for the temporal distribution, the sequential cropping index decreased from 2001 to 2003, whereas it increased slightly from 2003 to 2004. However, the index of arable land was relatively low, as far as the geographic position and climatic resource were concerned, and the potential of the sequential cropping index was great.

陕西省NDVI时空变化及其对气候和人类活动的响应

利用2001—2020年MODIS NDVI数据,结合降水、气温等资料,采用Sen趋势分析、Mann-Kendall检验、Hurst指数、Pearson相关分析以及多元回归残差分析等方法,研究陕西省近20 a归一化植被指数NDVI的时空变化特征及未来变化趋势,探讨省内气候因素及人类活动对NDVI变化的影响以及NDVI对降水和气温响应的时滞效应。研究结果表明:(1)2001—2020年陕西省NDVI整体呈上升趋势,增长速率为0.004 7/a,NDVI在不同生态区有所差异,空间异质性明显;(2)陕西省NDVI变化的反持续性强于持续性,未来NDVI变化趋势以反持续改善(退化)为主;(3)陕西省降水和气温对NDVI变化均产生了正向影响,且NDVI与气温的相关性强于降水;(4)陕西省NDVI对降水的响应不存在明显的时滞效应,对气温响应的滞后期以0~1个月为主;(5)陕西省大部分地区NDVI残差呈增大趋势,人类活动对植被覆盖变化起到了显著促进作用。

Spatiotemporal Changes in NDVI and Its Driving Factors in the Kherlen River Basin

Vegetation is an important factor linking the atmosphere,water,soil,and biological functions,and it plays a specific role in the climate change response and sustainable development of regional economies.However,little information is available on vegetation vulnerability and its driving mechanism.Therefore,studying temporal and spatial change characteristics of vegetation and their corresponding mechanisms is important for assessing ecosystem stability and formulating ecological policies in the Kherlen River Basin.We used Moderate-resolution Imaging Spectroradiometer(MODIS)normalized difference vegetation index(NDVI)remote sensing images from 2000 to 2020 to analyse temporal changes in NDVI with the autoregressive moving average model(ARMA)and the breaks for additive season trend(BFAST)in the basin and to assess natural,anthropogenic and topographic factors with the Geodetector model.The results show that:1)the long NDVI time series remained stable in the Kherlen River Basin from 2000 to 2020,with a certain significant mutation period from 2013 to 2017;2)the coefficient of variation(CV)in the analysis of the spatial NDVI was generally constant,mainly at the level of 0.01–0.07,and the spatial NDVI change was minimally impacted by external interference;and 3)temperature and precipitation are the key factors affecting the NDVI in the basin,and changes in local hydrothermal conditions directly affect the local NDVI.The results of this study could provide a scientific basis for the effective protection of the ecological environment and will aid in understanding the influence of vegetation change mechanisms and the corresponding factors.

青藏高原典型草地NDVI时空演变的季节差异及其气候驱动

基于全球库存建模和制图研究(GIMMS)第三代归一化植被指数(NDVI3g)产品和气象数据,利用一元线性回归模型、偏相关分析和显著性T检验,分析了1982—2015年青藏高原高寒草甸和高寒草原春、夏、秋季NDVI时空演变的差异特征及其与气候因子的关系。研究表明:(1)高寒草甸春、夏、秋季NDVI整体均无明显变化趋势,高寒草原春季和夏季NDVI均显著增加,变化速率均为0.0002/a(P<0.05),而秋季NDVI变化趋势不明显。(2)空间上,高寒草甸春季NDVI显著增加面积占比31.95%,集中分布在祁连山区和三江源区,夏季NDVI显著增加的面积占比32.12%,主要分布在祁连山区、三江源地区和一江两河流域;秋季NDVI显著增加的比例为24.59%,集中分布于祁连山区和一江两河流域。高寒草原春、夏、秋季NDVI显著增加的区域均集中分布于西藏自治区北部和柴达木盆地南缘地区,分别占比44.20%、43.09%和37.99%。(3)高寒草甸春季和秋季NDVI均与气温显著正相关,偏相关系数达0.41(P<0.05)和0.23(P<0.05),夏季NDVI与气温、降水量和太阳辐射均呈显著相关性,偏相关系数分别为0.35(P<0.01)、0.56(P<0.01)和-0.57(P<0.01);高寒草原春季NDVI与气温和降水量均呈显著正相关,且与降水量偏相关系数较高,为0.31(P<0.05),夏季NDVI与气温、降水量和太阳辐射均呈显著相关性,与降水量偏相关系数最高,为0.46(P<0.01),秋季NDVI与太阳辐射显著正相关。(4)空间上高寒草甸春季和秋季NDVI与气温呈正相关的像元分别占比76.50%和67.86%,集中于祁连山区和三江源区,夏季NDVI与降水量呈正相关的像元占比58.42%,与太阳辐射呈负相关的像元占比53.69%,均集中分布于祁连山区、三江源区和一江两河流域。高寒草原春季和夏季NDVI与降水量呈正相关的像元分别占比63.02%和67.62%,集中分布在西藏自治区西部和柴达木盆地南缘。研究可为保护青藏高原草地资源、管理高寒生态系统植被碳库以及推动青藏高原长效生态增汇提供科学依据。

Gini Index for Cities: A Preliminary Study on Regional Differences of Chinese City Size Distribution

City size distribution is of interest because of a number of key stylized facts, including notably Zipf's law for cities and the importance of urban primacy. But a new and more efficient method Gini index can be used for calculating regional city size distribution. This paper begins by developing a calculation method for the Gini index, dividing the whole country into 26 areas and then calculating each area's Gini index value. Based on these calculation results, this paper gives a preliminary study on regional differences of its city size distribution and the dynamics.