Documentation

Documentation Methodology

Data sources and technical specification

Solargis provides 2 solutions for surface albedo data:

  • Long-term monthly averages, and
  • Time series

Both solutions use MODIS albedo data products as the primary data source, although additional processing and error corrections have been carried out by Solargis.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is an instrument aboard the Terra and Aqua satellites. The orbits of the satellites around the Earth are so that Terra crosses over the equator from north to south in the morning. Aqua moves in the opposite direction, from south to north in the afternoon. The instruments cover the globe every 1 to 2 days.

Technical characteristics of Solargis albedo data products:

Characteristic

Long-term monthly averages

Time series

Data sources

MODIS (main): MCD43GF

MODIS (snow albedo): MCD43C3, MOD10CM, MYD10CM

ERA-5 (gap-filling)

NSIDC (sea ice)

Solargis (1km land-sea mask)

MODIS: MCD43A3

Diffuse fraction (D2G) from Solargis irradiance database

Spatial resolution

1 km x 1 km

0.5 km x 0.5 km

Temporal structure

Monthly-means (12) + annual-means (1)

Monthly-means from 8-days values (each day value is a weighted average based on a temporal window of 16 days)

Daily time series

Each day value is a weighted average based on a temporal window of 16 days centred in day 9

Time coverage

2006 to 2015, 10 years

Feb 2002 to present, 18+ years

Gaps in data

No

 Yes

Access

Solargis Prospect Pro

Upon request. A technical report is issued along with the data file.

 

Long-term monthly averages

The database of long-term average albedo values is of a set of 12 (monthly averages) +1 (annual average) maps that can be accessed via the Solargis Prospect tool. It provides gap-free albedo data at high resolution and with global coverage.

The gap-filled snow-free MODIS product MCD43GF has been used as the primary data source. However, since this MODIS product does not include albedo values for ephemeral snow, information from several MODIS products and ERA5 data has been combined to prepare a gap-free high-resolution dataset for all kind of land surfaces (including ephemeral snow). Finally, additional information was used to add the albedo of ocean ice, and to correct imperfections and errors related to imprecisions of the MODIS land-sea mask.

Time series

For Solargis time series of albedo, data sources that have a long historic record and reasonably high temporal resolution (at least daily values) are used. These include MODIS products MCD43A1 and MCD43A3. However, these products present missing data (data gaps), mainly due to persistent cloudiness.

The choice of data solution (monthly averages or time series) that should be used depends on project requirements. Typically, the use of the monthly average database is recommended in the pre-feasibility stage and use of time series is recommended in the due diligence phase. 

Some examples of situations when the use of time series is more appropriate include:

  • Satellite-derived albedo is to be compared with ground-based albedo measurements
  • Monthly average data may not be sufficient for considering individual stochastic events such as ephemeral snow. Only the averaged effect of such events is considered.
  • The land cover of the project location may have changed over time and an average of years 2006-2015 may not represent the current situation
  • The land cover at project location is quite heterogeneous, and a dataset with a spatial resolution of 0.5 km would give more representative results than a dataset having 1 km resolution