And now for something completely different – A Landsat for the 21st century
“For over 40 years, the Landsat program has collected spectral information from Earth’s surface, creating a historical archive unmatched in quality, detail, coverage, and length.” (Landsat web page) During that time incremental improvements have been made to the Landsat system, but no fundamental breakthroughs have been made in achieving and enhancing the basic mission.
The Landsat for the 21st Century originated from concepts described previously (Full Spectral Imaging, Empirical Reflectance Retrieval, and Autonomous Remote Sensing) and from the design of the High Spectral & Spatial Resolution Instrument (HSSRI). This design has also been incorporated into the Global Real-time Disaster and Environmental Monitoring Satellite (GRDEMSat). Major improvements to the Landsat system can be achieved by incorporating existing infrastructure and currently available, off-the-shelf technology that will fundamentally change the way the Landsat system operates while preserving all of its historical features. A key feature of the next-generation Landsat System will be that it collects information rather than data. The primary obstacle to implementation of this proposed system will be acceptance of the new ideas by the traditional user community.
Landsat Mission Objective
As its name suggests, the mission of Landsat is to maintain a record of the Earth’s land surface and to detect and monitor changes. After many years of operation, and including supplemental information, a very good record (archive) of the Earth’s land surface has been obtained. The day-to-day operation of Landsat then, is primarily in the detection and monitoring of change.
Earth observation from space must answer three questions; What?, Where?, and When? The Landsat archive provides an enormous trove of information regarding the What? and the Where? Using the archive facilitates the answering of the first two questions when new data is acquired. The archive also provides information about where to look for new data to monitor change, and therefore to maintain the archive with respect to the final question; When?
Rather than periodically acquiring images of the entire Earth and leaving it to the users to detect changes, it would be more practical to monitor only those portions of the Earth’s land surface that have changed. This means collecting information (change) rather than data (mostly what you already know). This can be done operationally by targeted monitoring using a full function next-generation Landsat instrument system, and by employing alternative sources of information. By requiring only relatively small portions of the Earth’s surface to be monitored frequently, significant gains can be made in information quality, usability of the information, and in reliability of the sensors. The new system design is also expected to significantly reduce the system cost.
For change detection, rather than using a single satellite with a wide swath coverage, it is more practical to use a constellation of satellites with narrow coverage and off-nadir pointing capability. A five satellite constellation, for example, would allow imaging of any place on Earth at least once per day. NASA has favorably reviewed this option. Similar systems are currently operational and in development (see Landsat Alternatives at Landsat for the 21st Century.
Landsat Instrument System
To maximize spectral, spatial, and temporal resolution a dual imaging system and instrument pointing can be used. Maximum spectral resolution can be achieved using a Hyperspectral (or preferably a full spectral) imaging system. Maximum spatial resolution can be achieved with a Time Delay and Integration (TDI) multispectral system. Each imager would use the same fore-optics and have the same swath width, about 40 Km.
Temporal resolution would be maximized employing the five satellite constellation and instrument pointing. As described above, the Landsat mission can be accomplished by observing areas of change. To do this on a daily basis, the satellites must have the capability to slew cross track to observe areas of interest. The subject of target selection for change observation is a proven capability and is addressed elsewhere.
The capability slew the satellite along track can also be utilized to improve image quality or the signal-to-noise ratio. This is also a proven capability.
Landsat System Development
To exploit existing infrastructure and currently available, off-the-shelf technology, collaboration with several organizations will be required to develop the Landsat for the 21st Century. Organizations will be needed with expertise in instrument development, spaceflight program management, data acquisition, processing, archiving, and distribution, and finally, machine learning and/or Artificial Intelligence (AI). The lead organization for the Landsat for the 21st Century Program can come from any of these organizations.
Using currently available technology and infrastructure, and overcoming more than 40 years of conventional thinking would provide a Landsat system for the 21st century. This new system would provide improved spatial, spectral, and temporal resolution information and probably most importantly, it would make the information more readily available to users in a format that is easy to use. Without significant technological and operational improvement Landsat risks becoming a relic, primarily valued for its archive.
This page was last modified on 10 November 2015