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D&V Cube Full Guide

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Book: D&V Cube Full Guide
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Date: Friday, 19 April 2024, 5:55 AM

Table of contents

1. Introduction

The Drought & Vegetation Data Cube (D&V Cube) is a collection data records that are relevant for drought and vegetation monitoring. 

The D&V cubes contains variables from different providers:  

All data records were fit into a common data model i.e. all data in the cube are provided on a regular latitude-longitude grid (WGS84) and all files in the cube are in cf-compliant netcdf-4 format. Details on the methods used to bring the original data into this data model are provided in the methods document.

Information on the variables provided in the cube is provided in this guide. The fact sheets refer to the data records as they are provided in the D&V cube. The Product User Manuals, Algorithm Theoretic Baseline Descriptions and Validation Reports refer to the original data. Please note this, especially when referring to validation reports: most of the data records in the D&V cube have been regridded, which may have implications on the accuracy of the data. 

In the D&V cube you will find 2 different types of data records: 

  • Climate Data Records (CDRs) and 
  • Interim Climate Data Records (ICDRS). Both are explained in the short video below:

In short: 

CDRs are of highest quality, but their temporal coverage usually ends a few years before present. 

ICDRs fill the gap between the end of a CDR and present. There quality may not be as high as the quality of the corresponding CDR, but they do provide the best available quality of this data record of the time being. 


2. Global Radiation, Direct Normalized Irradiance and Sunshine Duration

Global Radiation (SIS) is the amount of incoming solar radiation (direct + diffuse). The acronym used here is SIS – solar incoming radiation at the Earth surface.  

Direct Normalized Irradiance (DNI): Direct Irradiance is the amount of sunlight reaching the Earth surface directly, without beeing scattered at clouds, aerosoles or other particles in the atmosphere. The direct normalized irradiance (DNI) is calculated as if it would reach the surface perpendicular. 

Sunshine Duration (SDU) provides the number of “sunny hours” per day or per month:  
SDU = Sunny slots / all slots during daylight * daylength.   
A slot is defined as sunny if the DNI > 120Wm-2.  Slot: pixel in each satellite image considered. Considered are ½ hourly instantaneous data. 
Daylength: period during which the sun elevation angle > 2.5°.  

All three variables, Global Radiation (SIS), Direct Normalized Irradiance (DNI) and Sunshine Duration (SDU) are provided by the CM SAF. They are derived from MVIRI and SEVIRI sensors on Meteosat first and second generations, respectively, using the SARAH-2.1 retrieval. 

The Climate Data Records of SIS, DNI and SDU cover the period January 1983 – December 2017. The Interim Climate Data Records of SIS, DNI and SDU provided in this cube cover the period January 2018 – December 2020. 


For a quick overview on these data records as provided in the D&V cube refer to: 

For further information please refer to: 


3. Precipitation

DOI: doi.org/10.5676/DWD_GPCC/MP_M_V2020_100 

The data record on precipitation in the D&V cube are provided by the Global Precipitation Climatology Project (GPCC).

Precipitation data from rain gauge measurements are collected, quality controlled and spatially interpolated. Here, the monthly sums or precipitation are provided. 


For a quick overview on this data record as provided in the D&V cube, refer to the: 

For further information, please refer to: 


4. Fraction of Absorbed Phytosynthetically Active Radiation, Fractional Vegetation Cover and Leaf Area Index

Fraction of Absorbed Phytosynthetically Active Radiation (fAPAR) 

Fractional Vegetation Cover (FVC) 

Leaf Area Index (LAI) 

fAPAR, the fraction of Absorbed Phytosynthetically Active Radiation (fAPAR), “represents the fraction of photosynthetically active radiation (400-700 nm) absorbed by the green parts of the canopy, and therefore constitutes an indicator of the presence and productivity of live vegetation. FAPAR depends both on canopy structure, leaf and soil optical properties and irradiance conditions.” (The EUMETSAT Satellite Application Facility on Land Surface Analysis Product User Manual Vegetation Parameters (VEGA), p 9) 

FVC, the fractional vegetation cover “represents the fraction of green vegetation covering a unit area of horizontal soil.” (The EUMETSAT Satellite Application Facility on Land Surface Analysis Product User Manual Vegetation Parameters (VEGA), p 9) 

LAI, the leaf area index “is a quantitative measure of the amount of live green leaf material present in the canopy per unit ground surface. […] LAI is a dimensionless variable [m2/m2] defined as one half the total leaf area per unit ground area and accounts for the surface of leaves contained in a vertical column normalized by its cross-sectional area. For non-leaves vegetation types, such as needles trees, LAI can be expressed as the total foliage surface area per unit of horizontally projected ground surface area.” (The EUMETSAT Satellite Application Facility on Land Surface Analysis Product User Manual Vegetation Parameters (VEGA), p 9) 

The Climate Data Records of fAPAR, FVC and LAI cover the period 19 January 2004 – 31 December 2015. The Interim Climate Data Record of fAPAR, FVC and LAI (see video) provided in this cube cover the period 01 January 2016 – 31 December 2020. 


For a quick overview on these data records as provided in the D&V cube, refer to: 

For further information, please refer to: 

 


5. Reference Evapotranspiration (MetRef)

MetRef (ET0), the reference evapotranspiration retrieved from METEOSAT “is the evapotranspiration rate from a clearly defined reference surface. The concept was introduced to allow the estimation of the evaporative demand of the atmosphere independently of crop type, crop development or management practices. ET0corresponds to the evapotranspiration from a hypothetical extensive well-watered field covered with 12 cm height green grass having an albedo of 0.23would experience under the given down-welling short-wave radiation (Allen et al., 1998).” (LSA SAF Product User Manual Reference Evapotranspiration (DMETREF), p.10) 

The Climate Data Record of MetRef covers the period 20 January 2004 – 31 December 2015. The Interim Climate Data Record of MetRef (see video) provided in this cube covers the period 01 January 2016 – 31 December 2020. 


For a quick overview on these data records as provided in the D&V cube, refer to: 

For further information, please refer to: 


6. Land Surface Temperature

LST, the land surface temperature represents the radiative temperature of the skin of the Earth Surface, as measure in the direction of the satellite sensor. “LST plays an important role in the physics of land surfaces as it is involved in the processes of energy and water exchange between the surface and the atmosphere.” (LSA SAF Product User Manual Land Surface Temperature (LST), p.12) 

The Climate Data Records LST covers the period 21 January 2004 – 31 December 2015. The Interim Climate Data Records of SIS, DNI and SDU provided in this cube cover the period 01 January 2016 – 31 December 2020. 

The data records on LST in the D&V cube are provided by the LSA SAF.


For a quick overview on these data records as provided in the D&V cube, refer to: 

For further information, please refer to: 


7. Normalized Difference Vegetation Index (NDVI)

NDVI, the Normalized Difference Vegetation Index is a measure of the “greeness” of the vegetation. It measures how much visible (red) light is absorbed by the vegetation in relation to how much near infrared light is reflected by the vegetation: 

NDVI = (NIR – RED) / (NIR + RED) 

The Climate Data Record NDVI cover the period 9 January 2007 – 31 December 2015. The Interim Climate Data Record of NDVI provided in this cube cover the period 01 January 2016 – 31 December 2020. 


For a quick overview on these data records as provided in the D&V cube refer to 

For further information please refer to: 


8. 2m Temperature

The 2m Temperature (T2m), is the air temperature 2m above the ground. Here the 2-m Temperature from the ERA-5 land re-analysis as provided in the Copernicus Climate Data store is used. 


For a quick overview on this data record as provided in the D&V cube, refer to the:

9. Soil Wetness Index (root zone)

DOI: 10.15770/EUM_SAF_H_0008 

The H141/H142 root-zone soil moisture product in the D&V cube is expressed as a liquid Soil Wetness Index (SWI), with units between 0 (residual soil moisture) and 1 (saturation), representing the lower and upper soil moisture limits. 

For the production of H141/H142, liquid SWI observations derived from ERS and ASCAT scatterometer data are bias corrected and assimilated in the H-TESSEL land surface model. After data assimilation, a post-processing step is then required to convert the volumetric soil moisture analysis into the H141/H142 liquid SWI. It is computed using the soil texture, the residual and saturated soil moisture, and the fraction of liquid water content (the fraction of water that is not frozen) on each grid point and each soil layer. Having the units of H141/H142 as a liquid SWI is consistent with the ERS and ASCAT soil moisture observations. The output consists of the liquid SWI in four different soil layers, down to a depth of 2.89 m. 

The Climate Data Record (H141) covers the time period January 1992 – December 2018. The Interim Climate Data Record (H142) covers the time period January 2019 – December 2020. Both products are provided by H SAF (http://hsaf.meteoam.it/). 


For a quick overview on these data records as provided in the D&V cube, refer to: 

For further information please refer to: