Remote sensing PART 2: Data sources, pre and post-processing tools.

Percepción remota parte 2: Datos,  herramientas de pre y post procesamiento

2. Where to get the data (global).

Next are provided links referred to Landsat, MODIS, ASTER, SRTM, TRMM data. Links to other kind of data are briefly referenced, either because the data is not public or simply because I have not used that kind of data.

2.1 NASA satellites.

A restricted budget has commonly been the major limitation for most profit and non-profit institutions. The acquisition of remotely sensed imagery is commonly expensive, and sometimes restricted given the understandable value of such kind of information. The NASA, through the USGS, has gradually agreed to release most of the data acquired by its satellites, which provide highly valuable information on the global earth surface processes.

a) Landsat missions: Provide the longest record (1972-present) of multispectral information available. Data is acquired every 16 days.

• Data retrieval: USGS EROS Data Centre, USGS Global Visualization Viewer.
• Data characteristics: GeoTIFF output format (after decompression), Cubic Convolution (CC) resampling method, 30-meter (TM, ETM+) and 60-meter (MSS) pixel size (reflective bands), Universal Transverse Mercator (UTM) map projection (Polar Stereographic projection for Antarctica), MAP (North-up) image orientation. More info here.
• Tools specific to convert/re project this data: None (I haven´t used any).
  
• Open source software: ERDAS View Finder (only viewing, saving, no processing), Ilwis (GIS and remote sensing), GRASS (GIS and remote sensing). For more links see here.
• Commercial software: ERDAS Imagine, ArcGIS, Adobe Photoshop.

b) MODIS Aqua and Terra: Records from 1999, daily time resolution.

• Data retrieval: Land Process Distributed Active Archive Center LP DAAC.
  
• Data characteristics: HDF output format, 250-meter (Bands 1–2), 500-meter (Bands 3–7), 1000-meter (Bands 8–36), projections vary according to the product. More info on the instrument here. More info on the products available here.
  
• Online tools specific for this data: Several.
  
• Open source software: Same as for the Landsat data.
• Commercial software: Same as for the Landsat data.

c) ASTER Global Digital Elevation Model DEM: Only this ASTER global data is released for public use. Other ASTER data may be accessible for certain organizations and institutions.

• Data retrieval: Land Process Distributed Active Archive Center LP DAAC.
• Data characteristics: GeoTIFF output format, 7 to 14-meter spatial resolution, WGS 84 projections. More info on the instrument and the products here.
• Issues: Cloud cover on mountainous regions (it is an optical instrument).
  
• Online tools specific for this data: I have only used the online sub-setting tool.
  
• Open source software: Same as for the Landsat data.
• Commercial software: Same as for the Landsat data.

d) SRTM DEM: This is the only global data released for public use. Other data may be free for certain organizations and institutions.

• Data retrieval: Global Land Cover Facility.
• Data characteristics: GeoTIFF output format, 90-meter spatial resolution, WGS 84 projections. More info on the instrument and the products .
  
• Online tools specific for this data: I have only used the online sub-setting tool .
  
• Open source software: Same as for the Landsat data.
• Commercial software: Same as for the Landsat data.

e) TRMM products:

• Data retrieval: Goddard Earth Sciences and Information Services Center.
  
• Data characteristics: HDF output format, 0.25 to 5 degree spatial resolution for gridded products, WGS 84 projections. More info on the instrument and the products .
  
• Online tools specific for this data: TOVAS TRMM Online Visualization and Analysis System.
  
• Open source software: Data can be provided in txt. format (coordinates, value format).

f) Brightness temperatures: For snow cover investigation through the Pathfinder Programme.

• Nimbus 7 SMRR Daily brightness temperature: Info and data retrieval here.
• DMSP SSM/I-SSMIS Daily brightness temperature: Info and data retrieval here.

2.2 Non-NASA satellites.

Even though NASA is the major institution in the field, several institutions have their own programmes throughout the world. However, their data is much more limited when compared to the information released by NASA.

- Advanced Land Observing Satellite ALOS (Japan).
- Others....