A sample WorldView-3 image (Image Credit: DigitalGlobe)

WorldView-3 is the latest satellite sensor from DigitalGlobe. With the addition of this sensor to its satellite constellation (in addition to QuickBird, WorldView-1, GeoEye-1, Ikonos and WorldView-2), DigitalGlobe will be capable of collecting ~1 billion km2 of Earth imagery per year. DigitalGlobe has added a SWIR (Shortwave Infrared) sensing 8-band instrument to WorldView-3 satellite that will open up a host of new civil and military applications.

WorldView-3 provides 31 cm panchromatic resolution, 1.24 m MS (Multispectral) resolution, 3.7 m SWIR (Short-Wave Infrared) resolution, and 30 m CAVIS ( Clouds, Aerosols, Vapors, Ice, and Snow) resolution. CAVIS will monitor the atmosphere and provide correction data to improve WorldView-3′s imagery when it images earth objects through haze, soot, dust or other atmospheric particles. WorldView-3 builds upon WorldView-2 and WorldView-1 technology by carrying forward the satellites’ advanced Control Moment Gyroscopes (CMGs). CMGs reorient a satellite over a desired collection area in 4-5 seconds, compared to 30-45 seconds needed for traditional reaction wheels(QuickBird e.g.).

Sensor specifications

PanchromaticPanchromatic: 450 – 800 nm
Multispectral (8 Bands)Coastal : 400 – 450 nm
Blue : 450 – 510 nm
Green : 510 – 580 nm
Yellow : 585 – 625 nm
Red : 630 – 690 nm
Red Edge : 705 – 745 nm
Near-IR1 : 770 – 895 nm
Near-IR2 : 860 – 1040 nm
SWIR Bands (8 Bands)SWIR-1 : 1195 – 1225 nm
SWIR-2 : 1550 – 1590 nm
SWIR-3 : 1640 – 1680 nm
SWIR-4 : 1710 – 1750 nm
SWIR-5 : 2145 – 2185 nm
SWIR-6 : 2185 – 2225 nm
SWIR-7 : 2235 – 2285 nm
SWIR-8 : 2295 – 2365 nm
CAVIS* Bands(12 Bands)Desert Clouds : 1195 – 1225 nm
Aerosol-1 : 405 – 420 nm
Green : 459 – 509 nm
Aerosol-2 : 525 – 585 nm
Water-1 : 845 – 885 nm
Water-2 : 897 – 927 nm
Water-3 : 930 – 965 nm
NDVI-SWIR : 1220 – 1252 nm
Cirrus : 1350 – 1410 nm
Snow : 2105 – 2245
Aerosol-3 : 1620 – 1680 nm
Aerosol-3 : 2105 – 2245 nm
*Clouds, Aerosol, Vapor, Ice, Snow

WorldView-3 has following other Design and Specification features. Particularly interesting are highest Pan resolution of 0.31m, 30m CAVIS bands and a locational accuracy of 3.5m CE90 comparable to the GeoEye-1

OrbitAltitude: 617 km
Type: SunSync, 1:30 pm descending Node
Period: 97 min.
LifeSpec Mission Life: 7.25 years
Estimated: Service Life: 10 to 12 years
Sensor ResolutionPan Nadir: 0.31 m(20° Off-Nadir: 0.34 m)
Multispectral Nadir: 1.24 m(20° Off-Nadir: 1.38 m)
SWIR Nadir: 3.70 m(20° Off-Nadir: 4.10 m)
CAVIS Nadir: 30.00 m
Dynamic Range11-bits per pixel Pan and MS
14-bits per pixel SWIR
Swath WidthAt nadir: 13.1 km
Attitude Determination and ControlType: 3-axis Stabilized
Actuators: Control Moment Gyros (CMGs)
Sensors: Star trackers, precision IRU, GPS
Pointing Accuracy and KnowledgeAccuracy: <500 m at image start/stop
Knowledge: Supports geolocation accuracy given below
Retargeting AgilityTime to Slew 200 km: 12 sec
Max Contiguous Area Collected in a Single Pass (30° off-nadir angle)Mono: 66.5 km x 112 km (5 strips)
Stereo: 26.6 km x 112 km (2 pairs)
Revisit Frequency (at 40°N Latitude)1 m GSD: <1.0 day
4.5 days at 20° off-nadir or less
Geolocation Accuracy(CE90)Predicted <3.5 m CE90 without ground control
Capacity680,000 km2 per day

As we can see from the table shown above, WorldView-3 sensor allows observation of a much wider range of the electromagnetic spectra than most other commercial satellites, and will allow the data user to start looking for the individual spectral signatures of materials. Below figure shows the spectral signatures of three minerals. The light blue regions on the plot denote the VNIR bands covered by Worldview-2and WorldView-3. The light red regions denote the SWIR bands covered by the 8 new WV-3 bands. This shows just how much further the new bands penetrate into the electromagnetic spectrum. The spectral profiles of each pixel in an image can be compared to a spectral library (such as the reflectance spectra shown) to classify what material is contained within that pixel.

This type of automated spectral classification allows us to remotely monitor materials and is invaluable to a great number of industries for example in forestry applications where we see users wanting to monitor tree health and pest infestation in remote regions. WorldView-3 brings a limited version of this capability to users at a reduced price, so one still can’t expect the accuracy of a hyperspectral satellite, but it really is a step beyond the features we could extract from multispectral data. Digital Globe’s marketing refers to this observation scheme as ‘super-spectral’.

Reference spectra of three minerals (Image Credit: Exelis)

CAVIS ( Clouds, Aerosols, Vapors, Ice, and Snow): The CAVIS imager is provided by Ball Aerospace & Technologies Corporation (BATC). The objective of CAVIS is to monitor the atmosphere and provide correction data to improve WorldView-3′s high-resolution imagery when it images Earth objects through haze, soot, dust or other obscurants. The CAVIS imager has a resolution of 30 m.

The CAVIS instrument brings an unprecedented level of consistency in data, paving the way to standardization of satellite imagery. CAVIS corrects for the inconsistencies caused by certain conditions, offering standardized imagery no matter where or when the data was captured. This standardization will introduce a new age of automated information extraction and feature detection.

The spectral window of WorldView-3 (Image Credit: DigitalGlobe)

Below shown animation portrays application of WorldView-3 imagery in identification of various minerals using ‘mineral indices’.

The spectral window of WorldView-3 (Image Credit: DigitalGlobe)

Application to Mineral Exploration (Image Credit: DigitalGlobe)

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