GeoCover LC - A Moderate Resolution Global Landcover Database

David J. Cunningham
Jeannine E. Melican
Eric Wemmelmann
Thomas B. Jones

Abstract

Earth Satellite Corporation (EarthSat) has developed two products based on Landsat data. GeoCover Ortho is a database of orthorectified Landsat TM scenes for the land masses of the world. This data is available from NASA, USGS, and EarthSat. GeoCover LC is a global landcover database derived from GeoCover Ortho imagery. This data consists of 13 landcover classes and is currently available for North America, Africa, the Middle East and Southwest Asia, and East Asia. This paper briefly describes the status of the project and the process used to create this data set


Introduction

Moderate resolution, resource-focused satellite remote sensing has been available since the launch of ERTS1, (later renamed Landsat 1) on July 23, 1972. Today, 30 years after the launch of the first Landsat satellite, the Landsat program continues to provide global moderate resolution, multispectral imagery. Imagery from the Landsat program has been, and continues to be used for a variety of applications in fields ranging from archeology to zoology. In fact "The data from the Landsat spacecraft constitute the longest record of the Earth's continental surfaces as seen from space. It is a record unmatched in quality, detail, coverage, and value." (NASA)

In 1997 Earth Satellite Corporation (EarthSat) proposed to NASA's Earth Science Enterprise to tap into this vast archive and develop a consistent, geodetically accurate, moderate resolution image base for the Earth. The goal was to develop a global orthorectified image base and global landcover database that would help enable the exploitation of this incredible but largely untapped resource. In 1998 with funding from NASA and NIMA, EarthSat began to develop the GeoCover Ortho and GeoCover LC products.

The GeoCover Ortho product is based on circa 1990 (generally +/- 3 years) Landsat TM data that has been orthorectified to less than a 50 meter RMS error. This image base is then used to coregister late 1970's Landsat MSS data and circa 2000 Landsat ETM+ data. Once this project is completed there will be a consistently orthorectified image base from the 1970's, 1990's and 2000 (Landsat MSS, TM, and ETM+) available for all the land areas covered by the Landsat program. These data are available with no copyright restriction and can be obtained from the Land Processes Distributed Active Archive Center at EROS Data Center at http://edcimswww.cr.usgs.gov/pub/imswelcome/ EarthSat is also creating 6 degree wide by 5 degree tall (UTM zone) MrSID compressed mosaics of the imagery (bands 7, 4, 2). These mosaics can be downloaded from NASA at http://zulu.ssc.nasa.gov/mrsid/

The availability of a global orthorectified, geodetically accurate Landsat image base provides scientists, educators, and the public the most accurate, global, comprehensive, up-to-date data available. The GeoCover LC program extends the use of the imagery by extracting land cover information from this imagery. The landcover categories in the GeoCover LC product follow closely to those defined by Anderson et al. in his 1976 publication, "A Land Use and Land Cover Classification System for Use With Remote Sensor Data" (U.S.G.S. Professional Paper 964). Brief descriptions of the 13-landcover categories are shown below in Table 1.

Table 1. Brief Description of GeoCover LC Classes

Class Number/Color
Class Title
Definition
1
Forest, Deciduous Woody vegetation > 3 meters (10 ft) in height that lose leaves periodically due to changing seasons or moisture regimes. Canopy closure must be >35% (<35% = Category 3). Also included in this category are areas commonly referenced as "swamp" or forested wetland if dominated by a deciduous canopy.
2
Forest, Evergreen Woody vegetation > 3 meters (10 ft) in height that retain their leaves throughout seasons. Evergreen includes both needle leaf and broad leaf species. Some tree plantations may be included in this class. Canopy closure must be >35% (<35% = Category 3).
3
Shrub/Scrub Woody vegetation less than 3 meters (10 ft) in height, with both closed and open canopies. Minimum ground cover is 10%; conversion to forest occurs at 35% canopy coverage provided the trees are > 3 m in height. Areas of forest that have experienced burning (burn scars) are classified in this category.
4
Grassland (>10% ground cover) Grass and herbaceous areas. Category may include herbaceous wetlands if images are collected during dry season or periods of drought. Land cover types commonly referenced as savanna and open savanna are included in this category. Areas of grassland and scrub/shrub that have experienced burning (burn scars) are classified in this category. Golf courses will be included in this class unless they are completely surrounded by the "Man-Made, Other" class.
5
Barren/Minimal Vegetation (<10% ground cover) Includes sand dunes, desert, rock outcrops, bare soil other than bare agricultural land, and sparsely vegetated areas of grass and shrub. This category includes non-vegetated strip mines and quarries except where covered by development (urban/built-up) or water (water).
6
Man Made-Other, Urban/Built Up Cities, towns, wide roads, airports, other developed areas. Areas of non-urban cover within the urban fringe are only separated from the urban category if they exceed 25 ha (500 x 500 m if square or 307 pixels) in size and 2 pixels (58 meters) in width.
7
Agriculture, General All non-rice agricultural fields, both with crop or fallow; highly managed pastures and hay lands (but not grasslands commonly referenced as "rangeland"); complex mosaics of natural vegetation and cropland. Some orchards and tree plantations, such as palm or date plantations, may be included in this category.
8
Agriculture Rice/Paddy Paddy agricultural fields, mainly rice, that are seasonally inundated with water. Depending upon the season of acquired imagery, some rice paddies may be included in the "Agriculture, Other" class if the paddies are not flooded.
9
Wetland, Permanent/Herbaceous Emergent herbaceous wetlands, as well as other irregularly inundated areas that may not be vegetated, including: mud flats, saltpans, and playas. Vegetated herbaceous wetlands may be referenced as "marsh". Areas commonly referenced as "swamp", including forested wetlands, are not included in this wetland class. Forested wetlands, with the exception of "Mangrove" are included in one of the forest categories. Areas of burn scar within a wetland are included in this category.
10
Wetland, Mangrove Regularly inundated coastal areas that are covered by mangrove species. Areas of burn scar within a mangrove wetland are included in this category.
11
Water All type of water bodies, including rivers, lakes, reservoirs, ponds, bays, and estuaries. This categorization does not differentiate between these water classes.
12
Permanent or Nearly Permanent Ice and/or Snow Areas covered by permanent or nearly permanent ice and/or snow.
13
Cloud/Cloud Shadow/No Data Areas in which the ground surface is masked by cloud, smoke, or thick haze, or their concurrent shadows. Also includes any area for which no meaningful Thematic Mapper signal is received, e.g., line drops, areas outside of the coverage of the outermost TM image footprint.

Landcover Extraction Process

The goal of the GeoCover LC program is to provide a fairly basic landcover classification but prepare it in a way that is accurate, consistent, and global. Extracting this information from moderate resolution Landsat imagery is a enormous task; over 7,600 scenes must be processed. In order to process this much imagery consistently, accurately, and efficiently EarthSat focused on three important aspects. First, automate as much of the process as possible; second, rely on time-tested image processing and analyst-driven interpretation to extract the land cover information; and third, implement continual quality control and process improvement to produce the highest quality product within stringent time and budget constraints

EarthSat's land cover extraction process relies heavily on commercial software (ERDAS IMAGINE, and Esri Arc/INFO) that has been customized by EarthSat personnel to improve production efficiency. The following is a brief description of EarthSat's procedure.

Unsupervised classification techniques are used to produce a thematic image with 240 spectral clusters. EarthSat uses IMAGINE's ISODATA clustering algorithm to generate the spectral signatures. These signatures are then run through a maximum likelihood classifier to produce a thematic image.

Skilled image analysts work in geographically focused teams to group and edit 240 spectral classes into 13 landcover categories (shown in Table 1.) It is critical that all image analysts work in a team environment, communicating as they research ground truth databases, visualizing and discussing imagery, consulting with senior remote sensing scientists, and working together to analyze spectral and spatial relationships necessary to extract land cover from imagery. Synthesizing a variety of disparate and oftentimes conflicting sources (including existing land cover, ground truth, information from adjacent scenes, and any other source of ancillary data) and incorporating both spectral and spatial relationship found in the imagery is the strength of a trained image analyst and the key component in GeoCover LC processing.

Once an analyst has completed preliminary grouping and editing the scene is submitted to an independent quality control team for review. The QC team reviews each scene for individual class accuracy as well as consistency of interpretation between image analysts. After a scene has passed the individual scene QC inspection (often after multiple iterations) the scene is approved for further processing.

A landcover image mosaic is then created, integrating multiple Landsat scenes within a geographic area - typically all scenes within a UTM zone. This mosaic has a formal QC process to ensure consistency in areas of scene overlap as well as throughout the entire region. The landcover mosaic is then used to clip out individual scene as well as one degree by one degree cell products. Table 2 briefly describes the GeoCover LC final products that are available.

Table 2-Base GeoCover LC Products

Product Type
Projection, Minimum Mapping Unit (MMU)
Description
Delivery Format
Example Reference
Land Cover-Raster No MMU UTM on WGS8428.5 m for all classes Land cover raster file with no MMU, ERDAS IMAGINETM 8.4 format thematic file, Cell values will indicate the land cover codes. Arc/INFO GRID files available Landsat path/row basis Fig 1a: Example of a GeoCover LC Product before application of MMU
Land Cover Raster with MMU UTM on WGS8428.5 m for water (class 11); 1.4 ha for all other classes Land cover raster file with 1.4 ha MMU applied to all classes except water, ERDAS IMAGINETM 8.4 thematic file format. Cell values will indicate the land cover codes. Landsat path/row basis Fig 1b: Example of GeoCover LC product with MMU applied
Geographic One Degree Cell Raster Land Cover with MMU Geographic on WGS8428.5 m for water (class 11); 1.4 ha for all other classes Land cover raster file with 1.4 ha MMU applied to all classes except water ERDAS IMAGINETM 8.4 thematic file format, generated from mosaics of Product land above. Cell resolution sizes of 0.000277777778 decimal degrees (DD) for latitude & longitude between 50o North & South. Poleward of 50o North & South, latitude cell size will remain the same while longitude cell size will be 0.000555555556 DD. 1o x 1o latitude/ longitude cell basis N/A
Geographic One Degree Cell Vector Land Cover with MMU Geographic on WGS8428.5 m for water (class 11); 1.4 ha for all other classes Land cover vector file with 1.4 ha MMU applied to all classes except water, Esri Arc/INFOTM Interchange (*.e00) format. The 13 GeoCover LC categories will contain the corresponding feature codes (f-codes). 1o x 1o latitude/ longitude cell basis Fig 1c: Example of GeoCover LC product with vectors overlaid
Metadata N/A A metadata file is provided on a cell by cell and a regional basis. Cell products: one .met file per cell, zipped with raster or vector data files. Scene products: one .met file per region N/A



GeoCover LC Products
Figure 1. An example of GeoCover LC Products

The landcover product has been independently validated and has averaged over 72% accuracy throughout the world.

Product Status

In less than three years EarthSat has completed over 4,000 GeoCover LC scenes and over 12,000 one degree by one degree water masks. (See figures 2, 3, and 4 for data availability.) This is the most extensive landcover-mapping program conducted using Landsat data.

GeoCover LC 1990 Status
Figure 2. GeoCover LC circa 1990 land cover availability


GeoCover LC 2000 Status
Figure 3. GeoCover LC circa 2000 land cover availability



Figure 4. GeoCover LC water mask availability



References

Anderson, J. R., Hardy, E. E., Roach, J. T. and Witmer, R. E., 1976. "A Land Use and Land Cover Classification System for Use with Remote Sensor Data." U.S. Geological Survey, Professional Paper 964. Reston, VA.

Dykstra, Jon. "The GeoCover Ortho Program." GeoInformatics. Volume 4. January/February 2001. Emmeloord, The Netherlands. . p 26-29. httphttps://s3.amazonaws.com/webapps.esri.com/esri-proceedings/proc02/://www.geoinformatics.com/issueonline/issues/2001/01_02_2001/pdf_01_02_2001/p26_29_dijkstra.pdf

NASA. "NASA Celebrates the 25th Anniversary of Landsat, Remarks for the Congressional Record." http://geo.arc.nasa.gov/sge/landsat/lsat25b.html


Author Information

David J. Cunningham,
Vice President, Environmental and GIS Services
email: dcunningham@earthsat.com

Jeannine E. Melican
Program Director, GeoCover LC
email: jmelican@earthsat.com

Eric Wemmelmann
Production Manager
email: ewemmelmann@earthsat.com

Thomas B. Jones
Former Program Director
email: tjones@earthsat.com

Earth Satellite Corporation (EarthSat)
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Telephone: (301) 231-0660
FAX: (301) 231-5020
http://www.earthsat.com
http://www.geocover.com