Evapotranspiration (AETI), Land Cover Classification (LCC), Net Primary Productivity (NPP), Precipitation (PCP), Phenology (PHE), Quality layers (QUAL), Reference Evapotranspiration (RET), Soil moisture (RSM), Total Biomass Production (TBP) and Water Productivity (WP)

Complementary Quality data layers

Quality layers indicate the quality of external data used to produce a data layer.

WaPOR data components

WaPOR provides quality layers for the NDVI and Land Surface Temperature (LST) inputs:
- Quality of NDVI: a decadal layer at both L2 and L3 that indicates the quality of external data used to produce the NDVI.
- Quality of NDVI long term: a single layer that indicates the long term quality of external data used to produce the NDVI
- Quality of LST: a decadal layer at L2 that indicates the quality of the Land Surface Temperature (LST) data

The NDVI quality layer not only represents the quality for the NDVI, but also for Evapotranspiration, fAPAR and NPP as these are calculated using the NDVI composites as input. LST is used to produce the decadal soil moisture stress data composites and thus has impact on the quality of evapotranspiration and biomass outputs.

Table 1: Overview of NDVI intermediate data component and complementary quality layer

Methodology

NDVI Quality layer

The quality layer is produced during the compositing of the NDVI. The quality index (QI) for every pixel in each dekad depicts the number of days since the last observation date used for reconstruction. When a number of consecutive dekads have not had direct observations for calculating the NDVI, the quality layer pixel value of the consecutive dekadal NDVI quality layers will represent the cumulative number of days since a valid observation. The user can use consecutive NDVI Quality layers to calculate the length of the gap between valid observations. In the case that the pixel observation is usable and no reconstruction was needed, the QI is set to 0 (ideal situation).

NDVI Quality layer long-term

An additional long-term NDVI quality layer is produced as a summary of the quality for the entire time period. Pixel values indicate the percentage of good NDVI observations over the entire time period. Whereas the dekadal NDVI Quality layer shows the quality of the data for a specific time of year, the long-term NDVI quality layer has been added to give users a quick overview of the areas that tend to suffer more cloud cover.

LST quality layer

Cloud cover causes data gaps in the input data required for the calculation of relative soil moisture content and soil moisture stress. Daily soil moisture is determined from daily LST images with cloud covered parts masked out. These daily images are then composited into dekadal data, taking into account the quality of the input LST layer (i.e. viewing angle and proximity to clouds). The Land Surface Temperature Quality layer indicates the number of days since the last observation, given on a pixel-by-pixel basis. The LST Quality layer is only produced for Level 1 and 2 because at level 3 Land Surface Temperature is obtained from instantaneous Landsat data which does not require compositing or interpolation methods.