2012_2022_VIIRS_Fourier Processed_1k_ER

Overview: This is a set of images produced by Temporal Fourier Analysis (TFA) of VIIRS data: 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 2022. Process: Image values were extracted from VIRRS imagery form 2012 to 2022. 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 output recorded the time series's mean, minimum, and maximum, and 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 in the same way. Projection + EPSG code:Latitude-Longitude/WGS84 (EPSG: 4326) File 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. 22 refers to the year timeline of 2012-2022.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 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.概述： 本数据集为对可见红外成像辐射计套件（Visible Infrared Imaging Radiometer Suite, VIIRS）数据开展时间傅里叶分析（Temporal Fourier Analysis, TFA）后生成的图像集： - 归一化植被指数（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多项关键环境指标，并纳入了季节动态特征。本系列VIIRS数据参照Scharlemann等人2008年的研究方法进行处理，现已更新至2012至2022年的影像数据。 处理流程： 从2012至2022年的VIIRS影像中提取各参数值。日间与夜间地表温度数据取自8天合成的VNP21A2数据集，而植被指数与中红外波段数值则从16天合成的VNP13A2数据集中提取。随后针对每一项参数的提取数据集，通过时间傅里叶处理算法开展运算。采用逐级阈值筛选与插值方法，剔除时序序列中的错误值并填补数据空白。对平滑后的序列以5天为间隔进行采样，并转换为一组正弦曲线，用以描述年际、半年际与季度际波动。针对每一组曲线，傅里叶算法将生成表征振幅、相位与方差的图像。其余输出结果则涵盖时序序列的均值、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海陆掩膜图层剔除海洋像元，并将影像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。本全新VIIRS数据集为MODIS TFA产品的更新与延续版本，可沿用该产品的使用方式。 投影坐标系与EPSG代码：经纬度/WGS84（EPSG: 4326） 文件名规则： 各文件名前缀“er”代表该影像覆盖E4warning研究区域内的欧洲及北非全域，且采用地理投影。“22”代表数据的时间跨度为2012至2022年。后续两位字符代表波段： 03：中红外波段 07：日间地表温度 08：夜间地表温度 14：归一化植被指数（NDVI） 15：增强型植被指数（EVI） 文件名最后两位字符代表傅里叶处理的输出类型： a0：均值 mn：最小值 mx：最大值 a1：年周期振幅 a2：半年周期振幅 a3：季度周期振幅 p1：年周期相位 p2：半年周期相位 p3：季度周期相位 d1：年周期方差 d2：半年周期方差 d3：季度周期方差 da：年、半年、季度周期总方差 vr：原始数据方差 各参数傅里叶变量的图像数值规则如下： - 中红外（03波段）：A0、A1、A2、A3、最小值、最大值、vr，反射率数值需乘以10000 - 地表温度（07为日间、08为夜间）：A0、A1、A2、A3、最小值、最大值、vr，（摄氏度+273）需乘以50 - NDVI（14波段）与EVI（15波段）：A0、A1、A2、A3，指数值需乘以1000 - NDVI（14波段）与EVI（15波段）：A0、最小值、最大值，指数值需乘以10000后加10000 - NDVI（14波段）与EVI（15波段）：vr值需乘以10000 - 所有类型：D1、D2、D3、Da为百分比值 - 所有类型：E1、E2、E3为百分比值 - 所有类型：P1、P2、P3为月份数值×100（1月对应100） 全球范围文件可在此处获取。