TerraColor PLUS White Paper

Transcription

1 TerraColor PLUS White Paper by Earthstar Geographics LLC TerraColor PLUS is a seamless, simulated natural color satellite imagery dataset covering the entire earth developed by Earthstar Geographics LLC. Originally released in 2005, the product has undergone continual enhancements and upgrades that make it the premier 15-meter resolution global dataset available today. This document explains many of those upgrades and enhancements and serves as a guide for comparing TerraColor PLUS to other 15-meter products. All the global 15-meter global satellite imagery products on the market today were created from a single source, the Landsat 7 satellite imagery processed for NASA's Earth Science Enterprise Scientific Data Purchase Program and released to the public domain in This high quality dataset serves as an excellent base for third-party vendors to build a 15-meter dataset with global coverage, but requires significant processing and enhancement to make it suitable and easy to use for most satellite imagery applications. Many of the 15-meter products on the market look similar at first glance, so what makes TerraColor different? Seamless, high quality imagery Ocean cloud and ice masking and fill Optional bathymetric relief shading 15-meter Antarctica imagery Complete global coverage Significant upgrades to the original source imagery Free ongoing imagery upgrade program 1

2 Seamless, high quality imagery When creating TerraColor, we tried to the highest quality global satellite imagery product possible with vibrant yet natural looking colors, and excellent overall contrast and clarity. It is also very important to blend seam lines between images to remove harsh transitions, and to correct of errors in the source data such as streaks and scan line errors where possible. Many of the other vendors have not taken the time to fix seam lines or correct errors, and the results show when you look at their products in detail. Does it really matter whether the imagery has obvious seam lines or whether islands are missing? To us, it does matter. Because of this, we are glad to provide samples of any area upon request for comparison with the imagery from other vendors. Original with seam line (left), and TerraColor PLUS with seam line repaired (right) 2

3 Ocean cloud and ice masking and fill One of the main issues with a global satellite imagery dataset is dealing with the clouds, ice and image edges in ocean areas that distract from the clarity and utility of the overall dataset. Most vendors have chosen not to address this issue, because the process of building an accurate global land/ocean mask and processing the entire dataset through it are very complex and time consuming. In 2007 Earthstar Geographics developed our own global land/ocean mask at 15-meter resolution. This mask defines the extent of all land areas, and also masks out areas with seasonally changing ice cover in the polar areas. We then applied the mask to our base TerraColor product and filled the ocean areas with a natural blue ocean color to create TerraColor PLUS. The mask fits tightly to most land/ocean interfaces, but also extends outward where needed to retain important near-shore information such as transitions of major rivers into ocean, and shallow water bathymetry and coral reefs. The mask also has a soft, feathered edge to smoothly blend the transitions between the land areas and the ocean fill. TerraColor PLUS western Iceland with ocean mask and fill (left) and original (right) Most global 15-meter imagery products look fairly good when zoomed out, but zoom in closer and you'll often see the edges of Landsat scenes and cloudy areas outlining most of the continents and islands. TerraColor's ocean masking provides a clean global image that makes it easy to use off-the-shelf for a wide variety of applications. The imagery is ideal for tracking vessels and aircraft over ocean areas, flight simulations, print and media applications, and identifying small islands that may be hidden among cloud cover. An alternate version of TerraColor with a global bathymetric shaded relief in the ocean areas is in development. 3

4 Optional bathymetric relief shading Using our proprietary 15-meter resolution ocean mask, we have developed two versions of TerraColor: one with a blue ocean fill color and another with a bathymetric color shaded relief image. Pricing is the same for both versions, however data volume is different. TerraColor with bathymetric shaded relief (left) and generic blue ocean (right) The following details can help you choose which version might be most suitable for your applications: Bathymetric shaded relief version - This version fills the ocean areas with a color shaded relief image Earthstar Geographics generated from gridded sea floor topography data. The color palette used was held to a relatively small range of colors to stay within a generic ocean color range and provide a smooth transition to water colors close to land areas. This version of TerraColor adds interest to global and regional views, and provides information on the geology of plates, continents and islands. Since data for ocean areas with no land must be provided with this version, the overall volume of imagery (file sizes) can be significantly larger than the generic ocean color version, especially for the complete globe. The shaded relief image used to fill TerraColor ocean areas was created from version 12.1 of the Measured and Estimated Seafloor Topography dataset developed by Scripps Institute of Oceanography (with their permission). The spatial resolution of the bathymetric data is one kilometer (1000m), so it is not nearly as detailed as the TerraColor 15-meter satellite imagery. (The 1Km bathymetry image has been smoothly resampled to 15-meters during processing, so pixels are the same size as TerraColor's.) 4

5 Blue ocean fill version - This version uses a generic blue ocean fill that may be preferable for some applications. These include smaller scale mapping where the ocean relief shading may be less desirable, flight simulations where the shading may be distracting, and when file size issues are important. Unlike the ocean shaded version, this version is generally shipped with only tiles containing some land data, so total data volume (file sizes) are smaller. (You can fill any empty areas with a blue background color for faster rendering in your application, or we can provide a set of ocean filler tiles to fill out the complete globe at no extra charge upon request.) 5

6 15-meter Antarctica imagery Does it really matter whether a global satellite imagery dataset includes Antarctica? We think it does, and if you look at the dataset displayed as a globe we think you'll agree because Antarctica covers almost 10 percent of the world's total land area. The NASA dataset did not include Landsat scenes covering Antarctica (as well as some other areas), even though Landsat coverage is available for much of the continent. In 2008 the U.S. Geological Survey released an orthorectified Landsat 7 coverage for Antarctica extending to 82.6 degrees South (where Landsat's coverage ends). Earthstar Geographics downloaded and processed this dataset, and incorporated it into our base TerraColor product, so we now have very high quality imagery of much of Antarctica. TerraColor PLUS provides complete coverage of Antarctica Where the Landsat coverage ends at 82.6 degrees South, we have blended in 125-meter imagery to fill the remainder. Imagery dates for the Antarctica coverage are which matches the date range of the NASA Landsat coverage. Other vendors either use low resolution 500-meter imagery for Antarctica (at best), or at worst have no data at all (a black hole ). 6

7 Complete global coverage Since Landsat coverage is not available for the entire globe, there is no 15-meter data for the polar areas. To fill this need, we seamlessly blended lower resolution imagery from the MODIS sensor onboard NASA's Terra satellite to fill these areas. (This is commonly available to the public in various versions of the Blue Marble product at 500-meter resolution). As a result, our TerraColor PLUS product provides true global coverage from pole to pole in one unified product, with almost no areas of missing data. We will continue to seek higher resolution imagery for the polar areas as part of our update program. Canada Landsat coverage extents (left), and TerraColor PLUS extended with 500m imagery (right) TerraColor PLUS provides complete pole-to-pole coverage in a single product 7

8 Significant upgrades to the original source imagery Unlike the static products offered by most of our competitors, TerraColor PLUS is a dynamic product. Since we built the initial version, we have been constantly upgrading and improving it to create the best possible product. We have done this using alternate Landsat scenes available from the original NASA data pool, and more recently with alternate Landsat 7 scenes available from the USGS public domain Landsat archive. The improvements include two main types: replacing or improving cloudy areas or areas with lower quality data, and adding 15-meter coverage of areas that were omitted from the original NASA source dataset. To create their original dataset, NASA selected one or two Landsat scenes for each area containing the least amount of cloud cover. However, although a scene may be 95% cloud free, there may still be significant cloud cover over certain land areas. We have tried to improve many of these areas by locating alternate scenes, processing all or parts of them, and seamlessly integrating the new areas into the TerraColor product. To date we have updated the quality of well over 100 areas of the world, including much of Ecuador, Calais, France, Lima, Peru and northern Hokkaido Island, Japan and many formerly cloudy islands are now nearly cloud free. Calais, France area original (left), and TerraColor PLUS upgraded with nearly cloud-free imagery (right) Santarskie Island, Russia TerraColor (left) and competitor data using original NASA mosaic imagery (right) 8

9 In addition to cloud cover, the original NASA dataset omitted coverage of many islands where Landsat coverage is available. We have attempted to add these islands to provide the most complete 15-meter global coverage available on the market today. Examples of islands that have been added include Jan Mayen (Norway), Bjornoya (Norway), Wrangel and Herald Islands (Russia), the South Sandwich Islands (UK), and Porto Santo Island, Portugal (which was completely cloud covered). It takes a lot of extra effort to improve a 15-meter imagery dataset covering the entire earth, but we believe it is worth it. Free ongoing imagery upgrade program As we continue to perform upgrades to TerraColor PLUS, any client purchasing our imagery will automatically receive upgrades of any areas they have purchased on a quarterly basis. This offer will be extended until Q4 2010, but may be continued beyond that. Client requests for upgraded areas will be prioritized and added to the projected update list. For questions, please contact: Earthstar Geographics LLC 1437 Morena Blvd #100C San Diego, CA Web: terracolor@es-geo.com Tel: Fax: