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is already undertaking right-looking operations.

      NASA contributions include the L-band SAR instrument, with a 12 m diameter deployable mesh reflector, 9 m deployable boom and octagonal instrument structure. In addition, NASA will deploy a high-capacity solid-state recorder (approximately 9 Tbits at end of life), GPS, a 3.5 Gbps Ka-band telecom system and an engineering payload to coordinate command and data handling with the ISRO spacecraft control systems.

      The ISRO will provide the spacecraft and launch vehicle, as well as the S-band SAR electronics to be mounted on the instrument structure. The coordination of technical interfaces among subsystems is a major focus area in the partnership. Orbit control within 350 m and a pointing control shorter than 273 arcseconds will enable good accuracy to follow deformation by InSAR.

      Data access: As mentioned by NASA (2019), the science teams and algorithm development teams at NASA and the ISRO will work jointly to create a common set of product types and software. The project will deliver NISAR data to NASA and the ISRO for archiving and distribution. NASA and the ISRO have agreed to a free and open data policy for these data. All NISAR science data (L- and S-band) will be freely available and open to the public, consistent with the long-standing NASA Earth Science open data policy.

      The target strategy assigns a single radar mode to a given area on Earth. Where target areas overlap, the modes are compatible so that no science discipline loses information. This set of global target types and associated radar modes will provide each of the individual disciplines with the data they need for their science. The observation plan calls for nearly continuous global coverage over land and ice. India has planned specific radar modes to fulfill ISRO’s science requirements for the mission. For the rest of the globe, the most inclusive radar mode was chosen where conflicting science discipline needs were identified.

      1.3.4. Biomass

      This mission has been selected as part of the ESA’s Earth Observation Program (Earth Explorer 7) and will be able to operate, for the first time in space, a P-band imaging radar at 70 cm wavelength. At this frequency (435 MHz), the ITU allocation is limited to a 6 MHz bandwidth: the program will address key information issues over forested areas, at low-resolution cells. A large circular antenna of 12 m will be used.

      Different applications are foreseen to exploit penetration through tropical forests, with SAR polarimetry and PolInsar interferometry as well as tomography. Different phases and orbit changes will be used along the mission to achieve different purposes and fulfill these applications, with different baselines from different orbits. The first option is a coverage with a double baseline using three interleaved swaths, a low repeat cycle and then a change of altitude to ensure a new coverage; complete coverage would need five months before coming back to the same tracks. The second option is a sub-cycle of three or four days, and a total cycle of 27 or 36 days, then a repetition every five months (Hélière et al. 2016). The coverage is determined by three adjacent stripmap modes with swaths of 60, 50 and 40 km, implying a roll maneuver to change swath (Arcioni et al. 2013).

      Launch is foreseen in 2023 in Kourou on a Vega launcher to put Biomass on a dawn–dusk sun-synchronous orbit about 600 km high.

      1.3.5. ROSE-L

      The Copernicus L-band ESA SAR Sentinel-1–2 radar mission, named ROSE-L (Radar Observing System for Europe), provides enhanced continuity for a number of Copernicus services and downstream commercial and institutional users. It should be launched in 2028 and will work in synergy with other Copernicus elements to specially address emergency management service requirements. It should offer the same coverage and same frame as Sentinel-1 (swath widths around 250 km) to exploit synergy with a repeat coverage of less than one day in Arctic areas, three days in Europe and six days everywhere using two satellites (Pierdicca et al. 2019). Spatial resolution is expected to be better than 5 m x 10 m.

      Data access: The main characteristics of the ROSE-L mission, dedicated to operational services, include reliability, data timeliness, a European free and open data policy, systematic acquisitions, a reduction in the number of payload modes and coordinated operations with Sentinel, and these distinguish ROSE-L from the other SAR mission initiatives.

1.4. Optical imaging missions

      1.4.1. Past optical missions

In this section, we present some optical satellites that have taken images that are considered as references today. These satellites were launched between 1984 and 2004. Most of them are inactive today (but not all of them). Such satellites were heavy, and many of them had considerable longevity. At the beginning of the 2000s, new satellites arrived, such as Ikonos and Quickbird-2: these were agile satellites, with submetric resolution and increased dynamic range. For various satellites, several parameters, such as altitude, local time, weight, year of launch, spatial resolution, panchromatic spectral range and swath, are given in Tables 1.6 and 1.7. As we focus on ground motion displacement measurements and DEM extraction, the highest spatial resolution (panchromatic band in general), with its corresponding swath, is given.

Table 1.6. Past mission characteristics and parameters

Satellite	Nation	Altitude (km)	Local time	Period of orbit (min)	Inclination (deg)	Weight (kg)
Landsat 5	USA	705	9:45	99	98.2	2,200
SPOT-1	France	822	10:30	-	-	1,907
SPOT-2	France	822	10:30	-	-	1,907
SPOT-3	France	822	10:30	-	-	1,907
SPOT-4	France	832	10:30	-	-	2,755
Landsat 7	USA	705	10:00	99	98.2	1,973
Terra ASTER	USA–Japan	705	10:30	98.88 Скачать книгу В начало < 11 12 13 14 15 16 17 18 19 20 > В конец