Earth Remote Sensing From the Space Station -- It's Not Just Handheld Cameras Anymore
Since the International Space Station became operational in November 2000, astronauts on board have taken more than 600,000 images of the Earth's land surface, oceans, atmospheric phenomena, and even images of the Moon from orbit using handheld film and digital cameras as part of the Crew Earth observations
Despite this large volume of imagery and clear capability for Earth remote sensing, the space station historically has not been perceived as an Earth Observation platform by many remote sensing scientists. With the installation of new facilities and sophisticated sensor systems on the International Space Station over the past two years -- and more to come -- this perception is changing.
So what can the station offer in terms of Earth remote sensing that free-flying, robotic satellite systems cannot?
Images with a variety of lighting conditions
Unlike many of the traditional Earth observations platforms, the station orbits the Earth in an inclined equatorial orbit that is not sun-synchronous. This means that the station passes over locations on the Earth between 52 degrees north and 52 degrees south latitude at different times of day, and under varying illumination conditions. Remote satellite-based Earth observing sensors are typically placed onto polar-orbiting, sun-synchronous platforms like Landsat7
in orbits designed to pass over the same spot on the Earth's surface at approximately the same time of day. These satellite platforms will revisit a location about every two weeks. While collecting imagery in similar lighting conditions is good for producing uniform data for a specific place, it restricts the time that data is collected (near local solar noon in most cases). If a scientist is interested in a surface process that typically happens in the early morning or late in the afternoon (for example, patterns in coastal fog banks), the data will be difficult to collect from the polar-orbiting sun-synchronous satellites.
Responsive Data Collection
Another advantage unique to the space station is the presence of crew that can react to unfolding events in real time, rather than needing a new data collection program uploaded from ground control. This is particularly important for collecting imagery of unexpected natural hazard events such as volcanic eruptions, earthquakes, and tsunami. The crew can also determine whether viewing conditions -- like cloud cover or illumination -- will allow useful data to be collected, as opposed to a robotic sensor that collects data automatically without regard to quality.
Complementing handheld, digital camera imagery taken by astronauts, the current automated sensor systems and facilities on board the space station -- both internal and external -- provide exciting new capabilities for Earth remote sensing. In addition, the station's power and data infrastructure
encourages the development of new sensors. The following systems managed by NASA for Earth observation are now or will shortly be onboard and operational for space station (or manifested for transport):
- Window Observational Research Facility , or WORF, provides a highly stable internal mounting platform to hold cameras and sensors steady while offering power, command, data, and cooling connections. With the WORF, the high-quality optics of the nadir viewing window -- looking "straight down" at the Earth -- in the U.S. Destiny Laboratory are now fully utilized for the first time.
- International Space Station Agricultural Camera, or ISSAC. The ISSAC was developed by students and faculty at the University of North Dakota. Its prime purpose is to collect multispectral data supporting agricultural activities and related research in the Upper Midwest of the United States. In addition the ISSAC also can be tasked to collect imagery of natural hazards and disasters in support of NASA humanitarian efforts. ISSAC collects information in the visible and near-infrared wavelengths (3 bands) at a nominal ground resolution of 20 meters perpixel.
- Hyperspectral Imager for the Coastal Oceans, or HICO, is mounted on the external facility of the Japanese Kibo module. The prime mission of HICO is to collect data on water clarity, bottom materials, bathymetry, and on-shore vegetation along the coasts of Earth's oceans at approximately 90 meters per pixel ground resolution. The sensor collects high-quality information in 87 bands over the visible and near-infrared wavelengths.
- International Space Station SERVIR Environmental Research and Visualization System, or ISERV is a planned sensor system consisting of a Schmidt-Cassegrain telescope paired with a digital camera system to collect visible-wavelength imagery at ground resolutions of less than 3 meters per pixel. The system will be mounted in the WORF, and have excellent stability and targeting capability. The sensor is intended to support the SERVIR program in its goals of humanitarian support by using Earth science data to aid the developing world, mitigate and respond to disasters, and provide humanitarian support.
Currently, individual science teams manage the access to data collected by the various sensor systems, but a central data access facility is planned for the future. The combined capabilities of both human-operated and autonomous sensor systems onboard the space station promise to significantly improve our ability to both monitor the Earth and respond to natural hazards and catastrophes. Integration of the space station Earth observation systems represents a significant and complementary addition to the international satellite-based Earth observing "system of systems" providing knowledge and insight into our shared global environment.
William L. Stefanov
Chief Scientist, Science Applications, Research and Development Department, Jacobs
NASA, Johnson Space Center