Table 4.4. Sources of currently operating panchromatic and multispectral moderate-spatial-resolution systems. (esriurl.com/IGT43 for current version.)
The USGS and NASA have collaborated on the creation of the Global Land Surveys datasets. Each of these collections was created using the primary Landsat sensor in use at the time, which were processed for either 5-year or 10-year periods with best available images.
WELD data. Global monthly and annual 30-meter global composites generated from contemporaneous Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Landsat 5 Thematic Mapper (TM) data for all non-Antarctic land surfaces are available for 3-year periods. Continental US and Alaska WELD data are weekly, monthly, seasonal, and annual 30-meter continental US and Alaska composites generated from Landsat 7 ETM+ data available for 10 years (2003 to 2012). Products are available through an interactive web interface or as hierarchical data format tiles from a direct download site.
MODIS is one of a number of instruments carried on the Terra platform, which was launched in December 1999. MODIS provides continuous global coverage every one to two days and collects data from 36 spectral bands (band designations). Bands 1 and 2 have a resolution of 250 meters. Bands 3 through 7 have a resolution of 500 meters. The remaining bands, 8 through 36, have a resolution of 1000 meters. The swath width for MODIS is 2,330 kilometers.
ArcGIS Online
ArcGIS Online dynamically serves the pixel values for eight bands (no thermal or panchromatic) of all scenes of moderate-resolution Landsat 8 imagery worldwide at no charge. It also serves the Landsat Global Land Survey composites of Landsats 1 through 7, created by NASA and USGS, of decadal Landsat imagery. In addition, ArcGIS Online serves multiple cached moderate- and low-resolution imagery from a variety of international space agencies.
ESA
The ESA’s Copernicus program is a combination of 30 multiple spectral resolution missions (Sentinels 1 through 6). Sentinel-1A and -1B (radar) and -2A and -2B (optical) have been launched and are operating successfully. https://sentinel.esa.int/web/sentinel/sentinel-data-access/access-to-sentinel-data.
Thermal Imagery — All Spatial Resolutions
Thermal sensors are a special type of multispectral scanner that sense only in the thermal wavelengths. Like radar imagery, thermal imagery is usually rendered in grayscale, with warmer areas represented by lighter shades and cooler areas in darker shades. The image can also be pseudocolored, with blue shades representing cool and red shades warm. Thermal sensors measure in wavelengths of electromagnetic energy that are naturally emitted from objects as a direct result of the objects’ temperatures. Thermal sensors do not measure reflected energy, but rather emitted energy, and therefore can be acquired any time of day or night. Because of issues caused by the atmosphere, thermal imagery is collected with wavelengths of either 3 to 5 microns, 8 to 14 microns, or both.
Thermal imaging sensors can be flown as part of a multispectral scanner or in conjunction with one. For example, the Landsat TM sensor (on Landsats 4, 5, and 7) has a thermal band of 10.40 to 12.50 microns in addition to sensing in the visible, near-infrared, and middle-infrared wavelengths. The thermal band has a spatial resolution of 120 meters on Landsats 4 and 5 and 60 meters on Landsat 7. Landsat 8 also has a thermal sensor, called the Thermal Infrared Sensor (TIRS), which flies on the same platform as the Operational Land Imager (OLI). The OLI senses in the visible, near-infrared, and middle-infrared wavelengths. TIRS has two thermal bands (10.6 to 11.2 and 11.5 to 12.5 microns) and a spatial resolution of 100 meters. All Landsat imagery including the thermal data is freely available for download from a number of USGS websites including Earth Explorer (http://earthexplorer.usgs.gov), Global Visualization Viewer (GloVis) (http://glovis.usgs.gov/next/), and Landsat Look Viewer (http://landsatlook.usgs.gov).
Similarly, the Moderate Resolution Imaging Spectroradiometer (MODIS) senses in 36 bands at varying spatial resolutions depending on the wavelength. There are six thermal bands; four in the 3- to 5-micron range and two in the 10- to 12-micron range. The spatial resolution of the MODIS thermal imagery is 1 km. Additional information about the acquisition of MODIS imagery can be found at http://modis.gsfc.nasa.gov. Finally, the AVHRR also senses in the thermal wavelengths including one in the 3- to 5-micron range and two in the 10- to 12-micron range. AVHRR imagery is provided free by NOAA through the Comprehensive Large Array-Data Stewardship System at www.class.ncdc.noaa.gov/.
Thermal sensors on aircraft can also be a component of a multispectral scanner. However, it is more common for the sensor to be a thermal sensor with multiple wavelengths being collected just in the thermal range. These sensors have been flown on fixed-wing aircraft and helicopters and most recently on UAS’s, otherwise known as drones. There are many applications for thermal imagery flown on an aircraft. Most notably, these applications include forest fire detection and measurement of heat loss from buildings. The US Forest Service and NASA have cooperated extensively on detecting forest fires using thermal imagery and have put thermal sensors on airplanes, helicopters, and most recently on UASs. Many utility companies employ thermal sensors to detect heat loss from houses to demonstrate where increased insulation or replacement of windows could significantly reduce heating costs. Other applications for thermal data include disaster mapping such as volcanic activity and sensing of large mammals (bears, moose, elk, etc.).
Hyperspectral Imagery — All Spatial Resolutions
Hyperspectral imagery is not generally available from remote sensing systems and is most often flown on aircraft for specific projects. While flown by both private and public agencies, the most well-known hyperspectral remote sensing system is NASA’s AVIRIS, which operates an optical sensor capturing the spectral radiance in 224 contiguous spectral bands with wavelengths from 400 to 2500 nanometers. AVIRIS has been flown from 1992 to the present on four aircraft platforms mostly over the United States and Canada. The AVIRIS archive can be searched and data can be downloaded from http://aviris.jpl.nasa.gov/alt_locator/.
The only civilian source of hyperspectral satellite imagery is collected by the Hyperion sensor operating on the Earth Observing 1 (EO-1) Extended Mission. It is able to resolve 220 spectral bands (from 0.4 to 2.5 μm) at a 30-m spatial resolution. The EO-1 satellite was launched November 21, 2000, as a one-year technology demonstration/validation mission. After the initial technology mission was completed, NASA and the USGS agreed to the continuation of the EO-1 program as an extended mission. The EO-1 Extended Mission is chartered to collect and distribute Hyperion hyperspectral and Advanced Land Imager multispectral products according to customer tasking requests. Archived Hyperion imagery is available for search and download from the USGS EROS (http://eo1.usgs.gov/products/search).
Sources for Imagery Collected from Active Sensors
Lidar
Lidar imagery provides a comprehensive, detailed, and precise picture of the elevation of the earth’s surface as well