Written by Major D. Dugovskiy; Originally appeared at Foreign Military Review #12 2019, translated by J.Hawk exclusively for SouthFront
United States have made efforts to obtain infrared (IR) imagery of Earth surface for over 60 years. Therefore the development of IR surveillance satellites is best traced using the example of the main US space systems used for Earth surface imagery using IR cameras, in chronological order of their appearance.
The beginning of Earth surface IR imagery using spacecraft can be dated to April 1, 1960, when the United States launched the Tiros 1 meteorological satellite from Cape Canaveral. Its payload provided the first images of Earth in the IR spectrum. While not up to modern standards, they proved feasibility of using IR imagery of Earth’s surface.
Tiros-1 was launched on behalf of NASA and the US Department of Defense. It was equipped with two TV cameras. The satellite spent 78 days in orbit and displayed capabilities in monitoring Earth’s cloud cover. Starting in 1962, Tiros-series satellites began continuous Earth surveillance.
The IR imagery provided by Tiros enabled tracking weather both during day and night. They provided 8-bit images providing 8-10 kilometer resolution. While the resolution was low, it was nevertheless possible to satisfy a number of meteorological demands. With time, IR-spectrum data collection improved, both in terms of resolution and temperature. For example, NOAA-series satellites built for the National Oceanic and Atmospheric Administration in the early 1970s provided spatial resolution of 6km and temperature resolution of 1 degree.
Improving thermal imaging technology led to radiometers recording Earth’s thermal radiation in several narrow spectral channels, in the range between 8 and 14 micrometers. For example, NOAA satellites’ Advanced Very High Resolution Radiometer (AVHRR) payload measures the Earth’s albedo in five relatively five spectral bands (central wavelengths of .6, .9, 3.5, 11, and 12 micrometers), with spatial resolution of 1.1km and temperature sensitivity of .1-.2 degrees Celsius, in an observation band spanning 2,500km, enabling complete Earth coverage in one day. Using several IR bands facilitates the study of Earth and other planets by recording surface land and water temperatures, identifying geological structures and of types of mountain formations on the bases of IR spectrometry.
NOAA satellites currently operating use two types of payload, AVHRR and an atmospheric sensing apparatus. Their main purpose is tracking cloud cover and measuring the Earth’s background thermal radiation. The data received by this apparatus allows one to calculate surface temperatures on land and water. Data collected by AVHRR apparatus of various generations over a period of over 20 years have been extremely important in studying climate change and the state of the environment.
The first GOES-series satellite, also built for NOAA, was launched into geostationary orbit in 1975. Two of these third-generation satellites are able to record imagery in 12-18 bands from .47 to 13.3 micrometers, with spatial resolution of .5km in the visible spectrum and 2km in the IR spectrum, and the ability to survey the entire visible Earth surface in 5-15 minutes.
1978 saw the launch of three satellites with IR apparatus onboard: SEASAT, HSIMM, and NIMBUS. These satellites gave new impetus to the creation of Earth imaging satellites.
The first satellite intended to monitor the oceans was the SEASAT, launched on June 27, 1978. It worked until October 10, 1978 and failed following a short circuit in the onboard electrical system. Its mission consisted of demonstrating its capabilities in the realm of monitoring oceanographic phenomena. SEASAT also collected data about wind and sea surface and its temperature, wave height, internal waves, atmospheric water, sea ice, and ocean topography. The payload consisted of five main instruments for collecting information on the ocean’s surface. The VIRR instrument collected IR images with 7km resolution.
HSIMM was part of NASA’s Explorer program. Being the first satellite of the program, it was intended to conduct round-the-clock all-weather imagery of Earth’s surface using the two-channel radiometer bearing the same name. The first channel allowed taking images in the visible and near-IR spectrum (.55—1.1 micrometers), and the second in the far-IR spectrum (10.5—12.5 micrometers). The radiometer permitted IR-imagery with spatial resolution of 500-600 meters, in a 715km-wide band.
One must also note that the satellite had no ability to store images on board, which meant they had to be transmitted in real time, when the satellite was within ground station receiving range.
1978 also saw the launch of Nimbus-7 to test various oceanographic and meteorological monitoring systems. Its payload consisted of 8 instruments, including the Coastal Zone Coastal Scanner (CZCS). The scanner was built by Ball Aerospace Technologies and was a multi-channel scanning radiometer. It allowed the collection of IR images in six channels, with resolution of 825 meters. CZCS was mainly used to image coastal waters and oceanic currents in the spectral zone centered around 11.5 micrometers. In the orbital nadir, the width of scanning band was 1,556 km.
Concepts utilized in CZCS became the bases of the next generation of oceanic IR scanners. SeaWIFS sensor was an evolutionary development, which in turn was followed by the MODIS IR spectroradiometer. SeaWIFS was installed on the Seastar satellite launched in 1997 was not intended to work in the IR spectrum. Using eight spectral channels, it allowed imagery with spatial resolution of 1,100 meters.
MODIS was installed on Terra and Aqua satellites, launched in 1999 and 2002, respectively. They conduct imaging in 36 channels: 12 in the visible spectrum, 8 in near and mid-IR, 16 in IR (including 6 in the 3-5 micrometer window, 8 in the 8-14 micrometer window, and 2 between them to study water vapor content in the atmosphere and clouds).
Two channels have resolution of 250m, five—500m, and 29 (including IR ones) 1000m, with the scanning width of 2300km. The scanner can conduct regular imagery of assigned territory.
MODIS data is in widespread use, as the system has many strong features. They include daily global Earth surveillance, large number of bands used in imagery, large number of channels with an average resolution. This data is used to ensure regular surveillance of natural phenomena such as cloud cover, aerosol concentrations, atmospheric water vapor, surveillance of dangerous weather phenomena, rapid cartography and studying ocean’s temperatures, sea ice cover, analysis and dynamics of phyloplankton spread to determine the ocean’s biological productivity, rapid automated location of forest fires, detection and monitoring of gas emissions and flares, high-resolution cartography of forest and agricultural productivity, monitoring of wetlands, salinity, floods, assessment of flood damage and of anthropogenic catastrophes on regional and global scale (including tsunamis, volcanic eruptions, etc.)
In addition to MODIS, Terra satellite also carries an improved Aster thermal radiation and reflectivity radiometer. This multichannel high resolution scanner allows imagery in both visible and IR spectrum.
Aster was created to permit more detailed and in-depth study of the Earth’s surface and atmosphere, as part of the US Eos program. This is a joint US-Japanese program, with Aster and ground signal receiving stations having been developed in Japan, and with NASA being responsible for the program’s management, satellite launches, and system development. Both parties partake equally in the receipt and dissemination of data.
Aster receives data in 14 bands: 3 in visible and near-IR, 6 in mid- and 5 in far-IR, with spatial resolution of 15, 30, and 90m, and each image covering a 60×60 km square. Near-IR data was not collected after early 2008 due to overheating of associated sensors.
Visible and near-IR bands are used to implement a broad range of monitoring and cartography tasks. Mid-IR bands are used to detect mineral deposits. IR bands are used to register thermal radiation from Earth’s surface and determine main types of mountain formations, surface temperature, detecting hot spots, monitoring volcanic activity, etc.
The largest US program in the realm of IR imagery is the Landsat space system. Since its inception in 1972, eight satellites have been launched. Landsat is the longest-endurance and successful dual-purpose Earth imagery program. The archive of collected images allows to analyze changes over the period of 40 years. The first two used the MSS scanner which allowed imagery in visible and near-IR spectrum. Landsat-3 which was launched in 1978 was the last first-generation satellite. Thanks to the improved MSS scanner it was the first satellite of the series which could perform imagery in far-IR spectrum with resolution of 240m. Second-generation Landsat-4 and -5 were fitted with two types of optronic scanners, improved Mss and newly developed Tm. Mss made it possible to take images in visible and near-IR bands with resolution of 80m, and Tm in visible, near-, and far-IR bands with resolution of 30m. Both scanners had resolution of 120m in far-IR bands. They could also ensure scanning width of 185km. The third generation of the series began with the loss of Landsat-6 in a failed launch, which carried the Etm scanner. During the development of payload for Landsat-7, Etm was modernized and received the designation Etm+. The main distinction of this instrument was the presence of a panchromatic channel with high resolution (15m) and improved spatial resolution in far-IR band of 60m. Landsat-7 has been in orbit since April 15, 1999.
Starting with June 2003, due to the failure of one of the imagery elements, Etm+ has been working improperly, leading to reduced quality of data. Imagery is received in the regime of switched off scan line correction. Landsat-7 problems forced the renewal of Landsat-5 use, which has been in orbit since 1984, but whose imagery has ceased in 2011 due to technical problems. The launch of fourth-generation Landsat-8, created as part of the Landsat Data Continuity Mission (LDCM), took place in February 2013. It carries the TIRS far-IR scanner allowing imagery in two bands: 10.6-11.2 and 11.5-12.5 micrometers, with resolution of 100m. Further R&D within the Landsat program is being conducted in order to create a next-generation satellite that would provide continuous Earth data with the required timeliness and resolution. NASA awarded the Landsat-9 development contract to Orbital ATK, which is now a subdivision of Northrop-Grumman. Currently the program is proceeding according to plan, however, in spite of low level of technological risk (most of the systems are borrowed from Landsat-8), the satellite has a number of novel features. Its far-IR TIRS-2 scanner will have a higher output level, and the OLI-2 scanner that’s under development will be similar to that created for Landsat-8, with minor changes. Thus TIRS-2, developed by the NASA Goddard Center will work in two far-IR spectral bands, with resolution of 100m. OLI-2 will take images in visible, near- and far-IR bands with improved precision (increased from 12 bits in Landsat-8 to 14 bits), which will slightly improve the signal-to-noise ratio. It will ensure resolution of 30m for all bands except for panchromatic, where it will be 15m. Both scanners are expected to be operational for five years, though Landsat-9 is expected to have life in excess of 10 years (the launch is planned for late 2021). Project cost was 885 million USD as of 2019.
One of the most classified US IR imaging satellite projects is the Sandia National Laboratory program under contract from the US National Nuclear Security Agency (NNSA). This program has resulted in the construction of the MTI satellite which was launched on March 12, 2000. It worked until November 2000 taking imagery of various parts of United States, after which its control system failed. Efforts to restore communications were undertaken in 2001 and 2003, but failed. MTI payload included a scanner for imagery of Earth’s surface in 15 spectral bands (three in visible spectrum, the remainder in near- through far-IR). The far-IR band utilized 8.0-8.4, 8.4-8.8, and 10.2-10.7 micrometer bands. Resolution of IR images was approximately 20m. According to the developers, its sensitivity was greater than any earlier satellite’s. It made it possible to register Earth’s albedo and thermal streams emitted by various parts of the surface. MTI also measured water vapor content and ice crystals and aerosols in the atmosphere to correct for the effects during the development of images. As far as the practical application is concerned. MTI data was expected to help with detecting run-off into rivers and lakes, chemical leaks, oil spots on water surface, mine “tailings”, monitor vegetation and volcanic activity. MTI were also used in scientific study of global changes. While the system was operational, it took images of various pieces of US territory, mainly to assess heat loss in powerplants. No data that was obtained by MTI is publicly available. One should also note that in order to conduct imagery from low orbits as part of the STP program, in 2000 USAF launched the Tse-5 mini-satellite with STRV-2 payload. Its development was financed by the US Ballistic Missile Defense Organization (BMDO). Instruments include a British IR camera weighing 23kg installed on the VISS anti-vibration platform developed by Honeywell, and can take images of areas 16x120km in mid-IR spectrum with resolution of 30m.
Therefore, given the large number of programs pursued by several US agencies with the aim of creating IR imaging systems over a long period of time, one can draw the conclusion that the US leadership is strongly interested in this matter and is allocating sizable funding to it. The most successful program of this kind is Landsat. This is confirmed by the fact that of currently operating IR-imaging satellites developed and used by the United States, the highest resolution (60m) is provided by Landsat-7 and its ETM+ payload, not counting the lost MTI satellite (20m) and Tse-5 satellite (30m) which have imaging apparatus of foreign manufacture.
The Landsat family has been for a long time a valuable source of data for geospatial research. ETM+ imagery apparatus is able to take images in visible, near-, mid- and far-IR bands, in addition to high-resolution panchromatic photos, which makes it possible to combine imagery data of different kinds in geospatial research, in order to achieve the best results. It’s evident that in some instances the resolution of 60m is insufficient, but as of 2019 higher-resolution IR scanners are not anticipated for use by civilian organizations, except for Landsat-9 with its improved IR apparatus but without significant improvement of resolution.