Contributor: Jeffrey Gillan

Sea Viewing Wide Field of View Sensor (SeaWiFS), SeaStar

GeoEye (formerly Space Imaging and OrbImage) and NASA

Launched in 1997, OrbView-2 provides daily images of the entire globe. It is mainly used for studying the ocean but has been used for other purposes such as terrestrial environmental monitoring and global crop assessment. The sensor collects data in 8 narrow spectral bands (6 color, 2 near infra-red) and has a broad spatial resolution of 1.13 km.

Its daily return interval is a major advantage for tracking fast changing surface conditions on a broad scale. Orbview-2 continually collects and archives data. A variety of products including radiance values, reflectance, and normalized differenced vegetation index (NDVI) are available. One major drawback for using this imagery is the cost. Each scene (1,500 x 2,800 km) costs $500. Alternatively, you can apply to become a NASA-authorized SeaWiFS user and get images for free. Given that imagery from two similar sensors, AVHRR and MODIS, are available at no cost, it is hard to see why OrbView-2 data would be used for rangeland applications.

Advanced Very-High Resolution Radiometer, MODIS - Moderate-resolution Imaging Spectroradiometer

_{Image source: SeaWiFS Project, NASA/Goddard Space Flight Center, and OrbImage}
Smoke over Montana and Wyoming.

Each of the OrbView-2 bands can gather data in two modes: local area coverage (1.13km resolution) and global area coverage (4.5km resolution). The images have a radiometric precision of 10-bits (i.e., data values range from 0 to 1,023 for each band).

OrbView-2 products are delivered in scenes measuring 1,500 x 2,800 km.

1997 to present

OrbView-2 is in a sun synchronous orbit at an altitude of 705 km above the Earth. It can revisit the same place on Earth every day.

If you are using the images for research of educational purposes you can apply to be an NASA-authorized SeaWiFS user and get free access to imagery. Instructions on how to do this are found here: http://oceancolor.gsfc.nasa.gov/SeaWiFS/LICENSE/checklist.html.

GeoEye sells OrbView-2 basic data sets in three processing levels. These basic data sets are not map projected or geo-corrected. The scene sizes are 1,500 x 2,800 km. The file sizes are approximately 30 MB and the cost is $500 per scene.

• Level 1A – raw digital numbers with radiometric and geometric calibration coefficients appended but not applied to the image
• Level 1B – top of atmosphere radiance
• Level 2 – Surface reflectance and NDVI

Products can also be purchased through many of GeoEye’s channel partners. Some of the companies sell higher processed products and some of the companies might sell images at reduced costs. A list of resellers can be found here: http://www.geoeye.com/CorpSite/Products/channel-partners/Default.aspx.

Because OrbView-2 is commercially operated, there are some licensing restrictions regarding image usage and sharing. Please consult with GeoEye to get the level of licensing that is appropriate for your research or project.

Complete product details can be found here on the GeoEye website: http://www.geoeye.com/CorpSite/products/imagery-sources/OV2_details.aspx.

All other information regarding Orbivew products is available on the GeoEye website: http://www.geoeye.com/CorpSite/.

OrbView-2 products are usually distributed in Hierarchical Data Format (generic HDF). This format can be reprojected or converted into other formats such as GeoTiff, but in the past HDF has been notoriously difficult to work with. Recent versions of ArcGIS (e.g., version 9.3) as well as ENVI can read the HDF format. A listing of some other tools that can be used to view and convert HDF images can be found at https://lpdaac.usgs.gov/lpdaac/tools, but be cautioned that most of these tools are not easy to implement.

There are no known examples of OrbView-2 data being used in a rangeland context. Examples of the types of applications that OrbView-2 data could be used are on the wiki pages for the similar sensors.

• NASA’s SeaWiFS website http://oceancolor.gsfc.nasa.gov/SeaWiFS/

• Jenson, John R. (2007), Remote Sensing of the Environment: An Earth resource perspective, second edition, Prentice Hall series in geographic information science, Upper Saddle River, NJ.

_{You must have an account and be logged in to post or reply to the discussion topics below. Click here to login or register for the site.}