Map Asia 2009

Abstract
When WorldView-2 launches in the fall of 2009, more than a new satellite will be launched. It will be the first commercial satellite to offer 8-band capability with unsurpassed accuracy, agility, capacity and spectral diversity expected. The four additional colour bands: Coastal Blue, Yellow, Red Edge and Near-Infrared 2 —enable the performance of more accurate classifications, better automated feature extraction, enhanced shoreline mapping and coastal analysis. WorldView-2 is the first high-resolution multi-spectral satellite to provide a Coastal Bluedetector (400-450nm) enabling it to see further into the water and support bathymetric studies around the globe. In addition, remote sensing of the shallow ocean floor will now become much clearer and analysts will be able to discriminate features more accurately and increase the scope of remote sensing applications. Current, accurate depth measurements will provide increased navigational security, and support detailed mapping and modeling applications.

1. Introduction
WorldView-2 (WV-2) is the first commercial satellite to offer 8 spectral bands, including the traditional VNIR bands and an additional 4 spectral bands. These new bands are uniquely chosen for a variety of applications including natural resource management, coastal mapping, infrastructure mapping, and others. The following sections discuss various advantages of WV-2 spectral bands on automated feature extraction and information extraction from multi spectral imagery.

2. Spectral Response Curves
The following chart shows a comparison of WV-2 spectral regions with QuickBird and WorldView-1.

Figure 1. Comparison of Spectral Bands

It is important to note that the WV-2 panchromatic band spectral range is designed to ensure that the pan band does not extend into the NIR region of the EM spectrum. This ensures that the visual representation of the pan band is comparable to B&W photographic film. The additional bands include a Coastal Blue band, Yellow band, Red Edge band and another NIR 2 band.

3. WV-2 Advantages

3.1 Spectral Bands
The following figure shows a plot of information/content extraction based on spectral and spatial dimensions of remotely sensed imagery. WV-2 with 0.46 m spatial resolution and eight spectral bands allows for automated feature extraction and increased thematic accuracy.


Figure 2. Information Extraction Based on Spectral and Spatial Resolution



Further, it is of importance to consider the phenomenology of the features that are being extracted to maximize the additional spectral bands of WV-2. Red Edge and Yellow Edge bands are primarily designed for natural resource management. Vegetation/plants response to stresses often is the onset of senescence which is observable by marked changes in leaf coloration or chlorosis. Leaf chlorosis occurs where there is reduction in concentration of green pigments (chlorophyll a and b) that are replaced by increased concentrations of red and yellow pigments (carotenoids). Red Edge Position (REP) shifts according to changes of chlorophyll content, Leaf Area Index (LAI), biomass and hybrids, status, age, plant health levels, and seasonal patterns. For healthy plants with high chlorophyll content and high LAI, the red edge position shifts toward the longer wavelengths; when it suffers from disease or chlorosis and low LAI, it shifts toward the shorter wavelengths. The Red Edge band is designed to identify these shifts in REP and can effectively be used to classify and distinguish different vegetation types and ages.


Figure 3. Vegetation Spectral Signatures and WV-2 Red Edge and Yellow Bands

Further, aquatic vegetation/chlorophyll is very sensitive to response around 700 nm and the Red Edge band can be used to detect low density aquatic vegetation. Similarly large amounts of ethane cause a decrease in plant height and an increase in reflectance between 575 and 600 nm. In hyper spectral analysis the ratio: R605/R760, is used to map different stress levels and we believe that the ratio of WV-2 Yellow Edge to Red Edge will enable the mapping of vegetation health. The Coastal band, in combination with Blue band, is designed to allow for modeling for atmospheric effects. In contrast, NIR 2 band is placed where it is less susceptible to atmospheric effects. This allows for better vegetative analysis and biomass studies. Further, the NIR 2 band is less sensitive to thermal effects as compared to the NIR band.

3.2 Stereo
WV-2 is a very agile satellite and can collect color stereo imagery in one pass anywhere on the globe. The stereo capability allows for creation of accurate DSMs and DEMs from WV-2 imagery.

3.3 Radiometric Quality
WV-2 spectral bands are designed to ensure high spectral fidelity and minimize spectral overlap with other bands. This provides for high radiometric quality as well as consistency with WV-2 multi spectral imagery. Further, WV-2 can collect large areas in one pass resulting in imagery that has high radiometric consistency across the AOI. This allows for efficient ortho-mosaic creation and color balancing by reducing the radiometric consistencies introduced due to varying collection times, seasons, look angles, and other factors that affect the radiometry.

4. Feature Extraction
Fundamental imagery components of high resolution satellite images include vegetation, water, shadows, bare soil, and built-up areas. With the industry standard VNIR bands, the high correlation between the visible bands, negatively affects the extraction of the above components of a multi-spectral image. WV-2 additional bands are expected to improve the effective decomposition of the image as well as extract more detailed information. The following figure shows an example of an urban scene and associated accuracy improvement of automated feature extraction using WV-2 bands.


Figure 4. Advantages of WV-2 Bands

We believe that the combination of spectral and spatial resolution of WV-2 bands allows mapping of landuse/landcover (LULC) features at Anderson Level III or higher.

The following sections describe various applications of WV-2 multi-spectral imagery:

4.1 Coastal Mapping
The Coastal Blue band in combination with Blue band allows penetration of clear water up to 45 feet. This allows for variety of coastal applications including bathymetric mapping, benthic mapping (mapping of sea floor, see figure 5), benthic habitat mapping such as sea grass, algae, kelp, oyster beds, and other SAV (Submerged Aquatic Vegetation). The Coastal and Blue bands can be used for water quality studies including mapping of turbidity, suspended sediments, and others.


Figure 5. WV-2 Simulated Color (R, G, Coastal) for Benthic Mapping, Oahu, Hawaii

4.2 Geologic Mapping
WV-2 Red Edge and Yellow Edge bands are ideal for many geologic applications. Figure 6. shows an example of spectral signatures of some geologic minerals and the spectral range of the two bands respectively:


Figure 6. WV-2 Red Edge and Yellow Edge Spectral Bands for Geologic Applications

These bands in combination with NIR bands can be used for geologic mapping.

4.3 Urban Planning
The 8 bands of the WV-2 satellite are well suited for variety of urban planning applications including mapping of Impervious Surface Maps (ISM), Urban Tree Canopy (UTC), Landuse/Landcover (LULC), and others. The combination of higher spectral bands with 0.46 m spatial resolution, are expected to allow end users to extract LULC features at Anderson Levels III and some Level IV features.

4.4 Bio-Fuel Mapping
The increasing demand for oil has resulted in research for identifying new sources of bio-fuels. In the United States, several weed species have been identified as potential sources for bio-fuel. The Yellow and Red Edge bands in combination with large collection capacity and frequent temporal revisit makes bio-fuel mapping more economically viable with the addition of WV-2

4.5 Oil & Gas
Yellow and Red Edge bands in combination with NIR bands are well suited for identifying carbons seepages for Oil & Gas exploration. Carbon seepages tend to change the spectral characteristics of surface vegetation that might result in increased Yellow Edge reflectance as compared to the surrounding vegetation. The NIR bands are useful in detecting changes in soil mineral composition due to carbon seepages from the ground. The VNIR bands are ideal for pipeline monitoring to identify any potential leaks, map encroachment, and others. On the upstream side, the derived LULC covers maps derived from 8 spectral bands can be used in route planning and selection, Environmental Impact Assessment (EIA) studies including mapping of re-vegetated areas, mapping of disturbed surfaces due to exploration activities, identifying abandoned mines, and other exploration activities. On the down stream side, various applications of WV-2 bands include Health Impact Assessment by identifying features such as potential breeding grounds for mosquitoes, urban growth patterns near O&G facilities, water quality, and other features.

4.6 Agriculture
VNIR bands along with Yellow Edge, and Red Edge bands can be used to identify different types of crops, crop health, various kinds of stresses, weeds, biomass, LAI, and other parameters that can be used for precision agriculture applications including site specific pesticide and fertilizer applications, smart or directed soil sampling, yield estimation, and others. The collection capacity of WV-2 allows for regional crop assessments for commodities markets.

4.7 Forestry
The 8 spectral bands allow for forest type mapping and in some instances can be used for tree species identification. The 0.46 m spatial resolution allows for mapping individual tree crowns for tree inventory applications, forest thinning, mapping illegal logging, forest fires, and other applications (note: due to US licensing regulations, imagery may not be provided to commercial customers at less than .50 cm resolution). WV-2 Yellow and Red Edge bands are ideally suited for identifying trees that are infested and can help in monitoring reforestation efforts.

5. Conclusions
WorldView-2, which is scheduled to be launched on October 6th, 2009, will be the first high resolution commercial satellite to offer 8-band capability. The four additional color bands—Coastal Blue, Yellow, Red Edge and Near-Infrared 2—are expected to enable the performance of more accurate classifications and better automated feature extraction. WorldView-2 is the first high-resolution commercial multispectral satellite to provide a Coastal Blue band for enhanced bathymetric studies around the globe. The Red Edge, Yellow and Near-Infrared 2 will also greatly improve spatial analysis capabilities for government agencies: state, local and civil government, natural resources, as well as humanitarian relief organizations and precision agriculture.