DOI: 10.5281/zenodo.11083559
title: 2020_2022_VIIRS_Fourier Processed_1k_ER

description: 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 2020 to 2022 and was produced to compare with previous three years' time series.

Process:

Image values were extracted from VIRRS imagery form 2020 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. 19 refers to the year timeline of 2020

-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)

Files can be accessed here as well.