TABLE 3.1 Observing Technology and Key Observables Associated with an Enhanced Program
|Observing Technology (Sensor)||Description of Data Produced||Key Observables||Typical Applications|
|Fine resolution optical, stereo||Optical imagery with submeter to 10-m resolution||Land cover, building footprints, transportation and utility infrastructure, coastal margins, land surface topography||Urban planning, impervious surface mapping, transportation maintenance, coastal zone management, wildlife habitat, topography, three-dimensional buildings|
|LiDAR||LiDAR altimeter and bathymetric measurements based on multiple returns||Land surface topography, forest canopy height and leaf area, built structures||Geomorphology and natural hazards, ice sheet volume, forest productivity and health|
|Hyperspectral imaging||Optical imagery with narrow spectral resolution contiguous channels||Physiological signatures of vegetation, mineralogy, snow grain size, water pollution||Land carbon fluxes, biodiversity, invasive species, snow hydrology, mineral exploration, volcano gas monitoring|
|SAR, InSAR||Active microwave (radar) data||Surface deformation, forest structure, soil moisture and thaw depth||Natural hazards, water management, climate impacts, deforestation|
NOTE: SAR, synthetic aperture radar; InSAR, interferometric SAR.
Landsat data stream can be greatly increased by exploiting newer technologies that observe the surface at finer resolution and incorporate more of the electromagnetic spectrum.
Primary among these modalities is the ability to observe the surface at finer resolution than Landsat’s tens of meters. Power, orbit, and data rate constraints restrict the total volume of data that any satellite can deliver, so it is not possible today to image the full Earth simultaneously at fine scale and rapid repeat times. Remote sensing sensor suites thus require a trade-off between spatial and temporal resolution. At the coarse end of the spatial scale, current technological limits permit the entire globe to be observed daily at spatial resolutions of 0.25 to 1.1 km, as by, for example, the NASA Earth Observing System and NOAA’s Suomi NPP (National Polar-orbiting Partnership). Limiting temporal coverage to every 8 days, the globe can be observed at 15 to 100 m by Landsat 7 and Landsat 8 working together at moderate resolution with orbits offset by 8 days. Extending to finer resolutions, specific local areas of about 200 km2 can be observed every 2 to 3 days at 0.5 to 2.6 m by commercial programs like –DigitalGlobe, or the entire Earth could be observed annually if customer demand justified such a strategy. If the surface regions of interest are smaller still, airborne sensors can supply data at fine spatial resolutions and regular repeat times of hours to days. Aerial photography is a viable industry, with many companies providing fine-resolution panchromatic and multispectral images. Extending this to a national scale, the U.S. Department of Agriculture’s NAIP (National Agricultural Imagery Program) makes aerial imagery available to government agencies and to the public at no charge. Similarly, the aerial imagery in Microsoft’s Bing Maps is updated annually for the United States and Europe, and Google Earth provides a capability for other providers to upload imagery. A detailed summary of the spatial, spectral, radiometric, and temporal characteristics of all of the land remote sensing systems is not included in this report, but Figure 3.1 presents an abbreviated list of important moderate- and fine-resolution satellite remote sensing sensor systems from 1999 through 2015.
Landsat represents the current optimal trade-off between resolution, frequency of coverage, and global access constraints. Yet it is clear from Figure 3.1 that there are relatively few existing or proposed moderate-resolution remote sensing systems that can fill this critical need. The French SPOT 5 (2002), the Indian ResourceSat-1 (2003) and ResourceSat-2 (2011), Landsat 8 (2013), and the proposed Sentinel-2b (2014) and ResourceSat-2A are the most important operational systems. The foreign systems may provide useful data for U.S. users as long as the demands on the system are not too great. Without a Landsat-like U.S. instrument, the broad use of moderate-resolution imaging data and the gains of the exploitation of that data will suffer. The committee believes that maintaining the availability of such data is necessary if Earth is to continue to be observed frequently and with