2012_2020_VIIRS_FourierProcessed_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 has been updated to include imagery from 2012 to 2020. 

Abstract:

Image values were extracted from VIRRS imagery from 2012 to 2020. 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 mean, minimum, and maximum of the time series, 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 MOOD study region was a subset of global images. Idrisi rasters were converted to GeoTIFF format 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. 

File naming scheme:  

The er at the start of each file name indicates that the image covers the wider Europe and North Africa region included in the MOOD study area and is in geographic projection. 20 refers to the year timeline of 2012-2020.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 data

Files can be accessed here as well (including Global files). 

 Projection + EPSG code:Latitude-Longitude/WGS84 (EPSG: 4326)Spatial extent:Extent  -32.0000000000000000,10.0000000000000000 : 68.9999999999999574,81.9999999999999716Spatial resolution:0.0083333 deg (approx. 1000 m)  Temporal resolution: 8-day and 16-day  for 2012 to 2020 

Pixel values

Parameter 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)

Source:  VIIRS NASA :VNP21A2 and VNP13A2

Software used:Codes for modelling are in Python and C++The software used for map production is ESRI ArcMap 10.8

License: CC-BY-SA 4.0Processed by:ERGO (Environmental Research Group Oxford) https://ergoonline.co.uk/ for the H2020 MOOD project

数据集概览：
本数据集包含基于可见光红外成像辐射仪套件（Visible Infrared Imaging Radiometer Suite, VIIRS）数据经时间傅里叶分析（Temporal Fourier Analysis, TFA）生成的影像，具体指标包括：归一化差异植被指数（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）以及夜间地表温度（Night-time Land Surface Temperature, NLST）。
该影像集整合了季节动态特征，涵盖欧洲与北非区域的关键环境指标。本次更新后的VIIRS数据系列包含2012至2020年的影像数据。

数据集摘要：
影像数值提取自2012至2020年的VIIRS影像。其中昼夜地表温度数据来自8天分辨率的VNP21A2数据集，植被指数与中红外数值则提取自16天分辨率的VNP13A2数据集。随后，各参数提取数据集将通过时间傅里叶处理算法进行运算。研究采用逐步阈值与插值系统筛除错误数值，并填补时间序列中的数据缺口。经平滑后的序列以5天为间隔进行采样，并转换为一组正弦曲线，用于描述年际、半年际及季际波动。针对每条曲线，傅里叶算法将生成表征振幅、相位与方差的影像。其余输出结果则包含时间序列的均值、最小值、最大值，以及傅里叶变换过程中产生的误差。若需了解傅里叶算法及其输出结果的详细说明，请参考Scharlemann等人2008年发表的论文（https://doi.org/10.1371/journal.pone.0001408）。
研究利用VIIRS海陆掩膜图层对海洋像元进行掩膜处理，并将影像从正弦投影转换为地理投影。本数据集的MOOD研究区域为全球影像的子集。研究人员将Idrisi栅格数据转换为GeoTIFF格式，以提升数据使用者的操作灵活性。
本新型VIIRS数据集为MODIS TFA产品的更新与延续版本，可沿用该产品的应用方式。

文件命名规则：
每个文件名前缀“er”表示该影像覆盖MOOD研究区域内的欧洲及北非全域，且采用地理投影格式。“20”代表数据集的时间跨度为2012至2020年。后续两位字符用于标识影像通道：
03：中红外
07：日间地表温度
08：夜间地表温度
14：归一化差异植被指数（NDVI）
15：增强型植被指数（EVI）
文件名最后两位字符表示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：季周期振幅
p1：年周期相位
p2：半年周期相位
p3：季周期相位
d1：年周期方差
d2：半年周期方差
d3：季周期方差
da：年、半年及季周期总方差
vr：原始数据方差

用户可通过指定链接获取全部文件（包含全球范围影像）。

投影与EPSG代码：
经纬度/WGS84（EPSG: 4326）
空间范围：(-32.0000, 10.0000) 至 (69.0000, 82.0000)
空间分辨率：0.0083333°（约1000米）
时间分辨率：2012至2020年期间采用8天与16天分辨率

像元数值说明：
各参数的傅里叶变量影像数值规则如下：
1. 中红外（03）：包含A0、A1、A2、A3、最小值、最大值、vr，反射率数值需乘以10000
2. 地表温度（07为日间、08为夜间）：包含A0、A1、A2、A3、最小值、最大值、vr，数值为（摄氏度+273）×50
3. NDVI（14）与EVI（15）：
- A0、A1、A2、A3：指数数值×1000
- A0、最小值、最大值：指数数值×1000 + 10000
- vr数值：×10000
4. 所有参数的D1、D2、D3、da：以百分比形式呈现
5. 所有参数的E1、E2、E3：以百分比形式呈现
6. 所有参数的P1、P2、P3：月份×100（1月对应100）

数据来源：NASA VIIRS传感器的VNP21A2与VNP13A2数据集

所用软件：建模代码采用Python与C++编写，影像制图使用ESRI ArcMap 10.8

授权协议：CC-BY-SA 4.0
数据处理：牛津大学环境研究小组（ERGO, Environmental Research Group Oxford）为H2020 MOOD项目完成本数据集的处理工作，官网链接：https://ergoonline.co.uk/