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TerraLook is a free satellite image viewing tool. It provides access to satellite images for users that lack prior experience with remote sensing or Geographic Information System (GIS) technology. It does this by combining user-created collections of images on themes with a set of simple visualization and analysis tools, allowing the user to explore the data and employ it for useful purposes. The images include recent high-resolution ASTER images, and Landsat images from three historical periods going back to the early '70s. This historical data can support change analysis.

Access to satellite images has been largely limited to science communities with necessary resources like expensive software, tools and expertise. However, other types of disciplines including conservation, development planning, education, urban studies, or disaster planning and response could benefit from the ability to view and analyze chronologically and georeferenced satellite images. This type of data could be of particular use in developing countries that may have less capacity to purchase or work with remote sensing technology. This situation has resulted in the under-utilization of valuable data. Fortunately, these access hurdles can be overcome with tools like TerraLook. Google Earth, for example, has had a tremendous impact on the availability of image and vector data. However, it can be inappropriate for addressing certain types of questions such as those pertaining to change studies important to conservationists. Although Google Earth is very robust in its resolution and layering capability, bandwidth, time-series capability, and image processing options can be limited.

TerraLook consists of two parts: TerraLook Image Collections based on themes, and the TerraLook Software [1] to work with them. Image Collections. Users can create their own custom collections of images by visiting the USGS TerraLook website http://terralook.cr.usgs.gov/. Using the USGS Global Visualization Viewer (GloVis) [2], the images are selected, the collection built, and the user notified that it is available for download. Also, many standard collections have been archived and are available for download from the http://asterweb.jpl.nasa.gov/terralook.asp of this ASTER TerraLook website. Typically, these consist of country collections, containing full-country coverage with the historical Landsat images from 1975, 1990, and 2000, plus ASTER coverage of the Protected Areas of the country.


TerraLook was previously known as the Protected Area Archive, or PAA. That name reflects its origins, which lie in conservation, and the name was changed to better represent the broad range of user disciplines that it supports. The concept evolved out of discussions with Protected Area managers that began in early 2002, when the obstacles to use by these managers became apparent. The concept eventually led to a prototype being developed here at the NASA Jet Propulsion Laboratory with support from the ASTER Science Team. That prototype was demonstrated widely to obtain feedback, with the IUCN World Parks Congress (Durban, South Africa, 2003) being a major source of advice from a large number of park managers and conservation professionals. That led to an early version of the Viewer/Toolkit which was released a year later, at the IUCN World Conservation Congress (Bangkok, 2004), where additional feedback was obtained.

During this time the image collections were being generated on an informal basis at JPL. The USGS National Center for Earth Resources Observation Science (EROS) was then approached to discuss the possibility of their becoming the formal, operational host of the system. Funding was obtained from NASA and USGS to do this and work began on development of the formal, fully automated system. The operational system went "live" on 5 February, 2007.

In the meantime a more advanced, and Open Source, version of the Viewer/Toolkit software was being developed. The conservation NGO eCollage expressed an interest in working on the development, and funding was found from a World Bank sponsored project (the IABIN Connectivity Project) to do a proof-of-concept pilot, and, later, the next version of the Viewer/Toolkit. Version 1.0 of this software became available in February, 2007. Additional funds from a Gordon and Betty Moore Foundation project (the Amazon Basin Protected Areas Network) will support further development of this tool.

ASTER/JPL will continue to archive, and offer for download, the suite of "standard" collections [3] that it has previously created.

TerraLook Software

TerraLook Software is an Open Source Viewer/Toolkit and can be downloaded from http://terralook.sourceforge.net. The TerraLook Software was formerly known as the Protected Area Archive.

This tool includes the following capabilities:

Images From Four Sensors (satellites)

- ASTER: 2000 to present
- Landsat: c. 2000
- Landsat: c. 1990
- Landsat: c. 1975

Image Finder: Displays footprint (satellite) of images and outlines of protected areas so users can easily find and display images of interest

Roam and Zoom: To find and see features of interest within an image

Measure Distance and Area

Observing Change: Image "flicker" and side-by-side viewing

Overlay Manager: To create, edit, and control overlays, such as country and PA boundaries, add user-supplied overlays, read in shapefiles from a file, enter points into a table

Image Annotation: Adding text, lines, polygons, etc., so an image can be used to tell a story and effectively communicate an issue

Image Mosaicking: Combines multiple images into a single larger image.

Image Enhancement: Adjusts images to bring out desired features.

Multilingual: English and Spanish versions

Advanced Features: Band math, classify image, classify layer, attribute editing, 3-D viewing, more

TerraLook Image Collection Format

Collections utilize a simple format so they can easily be used by a variety of tools. GIS-savvy users can use their own tools if they prefer. The directory structure is as follows:


parameters.txt: Parameters used to generate the images. Most of these are for internal use only.

Terralook-Collection.xml: Collection level metadata in XML


This directory contains multiple shapefiles and text files that describe the footprints of the scenes in the collection. aster.shp: a set of boxes that outline the image boundaries for all images in the collection asterline.shp: a set of "X"s, one for each box, to help discriminate overlapping footprints for all images in the collection asterpoint.shp: a set of points that mark the centerpoint of each footprint for all images in the collection

image_layer.txt (aster.txt, Landsat--1990.txt, etc.): Tab Delimited text file for each image layer, detailing: Sensor Name Time of acquisition GMT (year, month, day, hour, minutes, seconds) Four Latitude Corner Location (Upper Left, Upper Right, Lower Left, Lower Right) Four Longitude Corner Location (Upper Left, Upper Right, Lower Left, Lower Right) Image file name image_layer-poly.shp: a set of boxes that outline the image boundaries for each image layer image_layer-line.shp: a set of "X"s, one for each box, to help discriminate overlapping footprints for each image layer image_layer-point.shp: a set of points that mark the centerpoint of each footprint for each image layer


This directory contains jpg images plus their corresponding world files to provide geocoding, and XML metadata.

image.jpg: The image file image.jpgw: The world file image.jpg.xml: Image metadata in XML image.txt: Image geographic summary /DEM

This directory may contain topographic data useful for 3-D visualization; otherwise it is left empty. The format is that used by the Global Land Cover Facility (GLCF).

External links