The most recent version of the specifications for the GlobalSoilMap.net
products (version 1.0 release 2.4
) as discussed and amended at the project meeting in Ottawa, Canada in November, 2015 are summarized here. The previous version of the specifications also can be accessed and downloaded from the link in the table below. The specifications do not prescribe how the products must be made; only what they need to conform to in order to permit collation and presentation of final standardized products.
The specifications focus on three aspects:
- the spatial entity,
- the soil properties to be predicted (and the date associated with their prediction) and
- the uncertainties for each soil property.
The spatial entity is a volumetric grid cell (or voxel) of specified horizontal and vertical dimensions and location. Each grid cell represents an area of 100 m by 100 m horizontal dimensions located at the centre point of a global grid of 3 arc-seconds by 3 arc-seconds. In the vertical dimension, predictions will be made to 2 m (if possible) with data reported for 6 depth intervals of 0-5 cm, 5-15 cm, 15-30 cm, 30-60 cm, 60-100 cm and 100-200 cm.
Ten soil properties will be predicted at each location. These are: (1) total profile depth (cm), (2) plant exploitable (effective) soil depth (cm), (3) organic carbon (g/kg), (4) pH, (5) sand (g/kg), (6) silt (g/kg), (7) clay (g/kg), (8) gravel (g/kg), (9) bulk density (Mg/m3) and (10) available water capacity (mm). Additional soil properties including ECEC (cmolc/kg) and EC (dS/m) may be predicted but these are not mandatory.
Each soil property will have an estimate of the uncertainty associated with the prediction for each depth for each grid location. Uncertainty is defined as the 95% prediction interval (PI), which is the range in values within which the true value at any prediction location is expected to be found 19 times out of 20 (95%). Methods of estimating uncertainty are not specified here but are outlined in a separate document.
A separate document will describe a series of recommended methods for producing the specified outputs. Selection of prediction methods is the responsibility of each node and is likely to vary from node to node and through time. Predictions may be produced at point support and subsequently averaged or aggregated to 100 x 100 m block support.
This current version of the specifications is presently still under discussion but is quite close to achieving final approval. This document provides the most current version of the complete specifications.