2012_2024_VIIRS_Fourier Processed_1k_ER

Overview: This is a set of images produced by Temporal Fourier Analysis (TFA) of VIIRS data (New version updated until 2024): NDVI: Normalised Difference Vegetation Index EVI: Enhanced Vegetation Index MIR: Middle Infra-Red DLST: Day-time Land Surface Temperature NLST: Night-time Land Surface Temperature The imagery summarises some key environmental indicators, incorporating seasonal dynamics, for the European and North African extent.This series of VIIRS data, processed according to Scharlemann et al (2008), has been updated to include imagery from 2012 to 2024. Process: Image values were extracted from VIRRS imagery from 2012 to 2024. The day and night land temperature came from the 8-day VNP21A2 data, whilst the vegetation indices and Middle Infra Red values were extracted from the VNP13A2 16-day datasets. Each parameter extract dataset was then processed by a temporal Fourier processing algorithm. A stepwise system of thresholds and interpolations screened erroneous values and bridged gaps in the time series. The smoothed series was sampled at 5-day intervals and transformed into a set of sine curves describing annual, bi-annual, and tri-annual fluctuations. For each of these curves, the Fourier algorithm generated images expressing the amplitude, phase, and variance. Other outputs recorded the time series's mean, minimum, and maximum and the error measured during the Fourier transform. For a detailed description of the Fourier algorithm and its output, please see the article by Scharlemann et al., 2008 (https://doi.org/10.1371/journal.pone.0001408)Sea pixels were masked with a VIIRS land/sea layer, and the images were projected from sinusoidal to geographic. The E4warning study region was a subset of global images. Idrisi rasters were converted to GeoTIFF format in order to give data users more flexibility. This new VIIRS Dataset is used as an update and continuation of our MODIS TFA product and can be utilised similarly. Projection + EPSG code:Latitude-Longitude/WGS84 (EPSG: 4326) Extent -32.0000000000000000,10.0000000000000000 : 68.9999999999999574,81.9999999999999716File names: The er at the start of each file name indicates that the image covers the wider Europe and North Africa region included in the E4warning study area and is in geographic projection. 24 refers to the year timeline of 2012-2024.The next two characters identify the channel:03 - middle infra-red07 - daytime land surface temperature08 - nighttime land surface temperature14 - NDVI: Normalised Difference Vegetation Index15 - EVI: Enhanced Vegetation IndexThe last two characters of each file name denote the output from the Fourier processing:a0 - meanmn - minimummx - maximuma1 - amplitude of annual cyclea2 - amplitude of bi-annual cyclea3 - amplitude of tri-annual cyclep1 - phase of annual cyclep2 - phase of bi-annual cyclep3 - phase of tri-annual cycled1 - variance in annual cycled2 - variance in bi-annual cycled3 - variance in tri-annual cycleda - combined variance in annual, bi-annual, and tri-annual cyclesvr - variance in raw dataParameter Fourier Variable Image values areMIR (03) A0, A1, A2, A3, Min, Max, Vr Reflectance values * 10000LST (07 day,08 night) A0, A1, A2, A3, Min, Max, Vr (Degrees Centigrade+273)*50NDVI (14) and EVI (15) A0, A1, A2, A3, Index Value * 1000NDVI (14) and EVI (15) A0, Min, Max, Index Value * 1000 + 10000NDVI (14) and EVI (15) VR Value * 10000ALL D1,D2,D3,Da PercentagesALL E1,E2,E3 PercentagesALL P1,P2.P3 Months*100. (Jan=100) Global Files can be accessed here.数据集概览： 本数据集为对VIIRS数据经时间傅里叶分析（Temporal Fourier Analysis, TFA）生成的图像集，本次为更新至2024年的新版本： 归一化差值植被指数（Normalised Difference Vegetation Index, NDVI） 增强型植被指数（Enhanced Vegetation Index, EVI） 中红外（Middle Infra-Red, MIR） 日间地表温度（Day-time Land Surface Temperature, DLST） 夜间地表温度（Night-time Land Surface Temperature, NLST） 该图像集涵盖欧洲与北非区域的关键环境指标，并纳入了季节动态特征。本系列VIIRS数据遵循Scharlemann等人2008年的研究方法进行处理，本次更新覆盖了2012至2024年的图像数据。 数据处理流程： 从2012至2024年的VIIRS影像中提取各参数值。日间与夜间地表温度数据源自8天周期的VNP21A2数据集，而植被指数与中红外波段数据则提取自16天周期的VNP13A2数据集。随后对每一项参数提取数据集应用时间傅里叶处理算法进行计算。通过逐级阈值筛选与插值流程，筛除时序序列中的异常值并填补数据空缺。将平滑后的时序序列以5天为间隔进行采样，并转换为一组正弦曲线，用以表征年际、双年际及三年际的波动特征。针对每一组曲线，傅里叶算法将生成对应的振幅、相位与方差图像。其余输出结果则包含时序序列的均值、最小值、最大值，以及傅里叶变换过程中产生的误差值。如需了解傅里叶算法及其输出结果的详细说明，请参阅Scharlemann等人2008年发表的论文（https://doi.org/10.1371/journal.pone.0001408）。 利用VIIRS海陆掩膜图层对海洋像元进行掩膜处理，并将图像投影方式从正弦投影转换为地理投影。E4warning研究区域为全球影像的子集范围。为提升数据使用者的操作灵活性，将Idrisi栅格格式转换为GeoTIFF格式。 本新版VIIRS数据集为原有MODIS TFA产品的更新与延续，可采用与后者一致的使用方式。 投影与EPSG编码：经纬度/WGS84（EPSG: 4326） 覆盖范围：-32.0000000000000000,10.0000000000000000 至 68.9999999999999574,81.9999999999999716 文件名规则： 文件名前缀'er'表示该图像覆盖E4warning研究区域内的欧洲与北非全域，且采用地理投影格式；字段'24'代表数据的时间跨度为2012至2024年。 后续两位字符用于标识数据通道：03代表中红外波段；07代表日间地表温度；08代表夜间地表温度；14代表归一化差值植被指数（NDVI）；15代表增强型植被指数（EVI）。 文件名末尾两位字符代表傅里叶处理的输出结果类型：a0代表均值；mn代表最小值；mx代表最大值；a1代表年周期振幅；a2代表双年周期振幅；a3代表三年周期振幅；p1代表年周期相位；p2代表双年周期相位；p3代表三年周期相位；d1代表年周期方差；d2代表双年周期方差；d3代表三年周期方差；da代表年、双年及三年周期的总方差；vr代表原始数据的方差。 各参数的傅里叶变量与图像数值规范如下： MIR（03）：A0、A1、A2、A3、最小值、最大值、vr，反射率数值需乘以10000 LST（07为日间、08为夜间）：A0、A1、A2、A3、最小值、最大值、vr，数值为（摄氏度+273）×50 NDVI（14）与EVI（15）：A0、A1、A2、A3，指数值需乘以1000 NDVI（14）与EVI（15）：A0、最小值、最大值，指数值需乘以1000后加10000 NDVI（14）与EVI（15）：vr值需乘以10000 所有参数的D1、D2、D3、Da均为百分比值 所有参数的E1、E2、E3均为百分比值 所有参数的P1、P2、P3均为月份数值×100（1月对应100） 全球范围数据集可通过以下链接获取。