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Satellite Imaging and Sensing
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Satellite remote sensing systems are also characterized by the different Earth orbiting trajectories of a given spacecraft. These two modes are usually referred as “polar orbiting” and “geostationary” (or “geosynchronous”) satellites. A polar orbit passes near the Earth’s North and South poles. Landsat, SPOT, and NOAA are near-polar satellites; their orbits are almost polar, passing above the two poles and crossing the equator at a small angle from normal (e.g., 8.2° for Landsat-4 and -5). If the orbital period of a polar orbiting satellite keeps pace with the Sun’s westward progression compared to the Earth rotation, these satellites are also called “sun synchronous.” This implies that a sun-synchronous satellite always crosses the equator at the same local sun time. This time is usually very carefully chosen, depending on the application of the sensing system and the type of features that will be observed with such a system. It is often a trade-off between several Earth science disciplines such as atmospheric and land science. Atmospheric scientists prefer observations later in the morning to allow for cloud formation, whereas the researchers performing land studies prefer earlier morning observations to minimize cloud cover.
Selling Space
Published in Dawna L. Rhoades, Evolution of International Aviation, 2016
Of course, all of this space activity requires a port to launch and return and there are a growing number of facilities hoping to fill this bill. The first question to answer is what does a facility need to be a spaceport, aside from governmental recognition. To answer this question, it is first necessary to understand the different types of orbits possible. There are essentially three types: geostationary, polar, and molniya. A geostationary orbit is a circular orbit at 22,236 miles (35,786 kilometers) above the Earth. An object in this type of an orbit has an orbital period equal to the Earth, thus it maintains a fixed position in the sky. This type of orbit is ideal for most communications and weather satellites. A polar orbit is one in which an object passes above both poles each revolution. Earth-mapping, observation, and reconnaissance satellites most often utilize this type of orbit. A molniya orbit
Satellite orbital parameters and outline satellite communication principles
Published in L. Tetley, D. Calcutt, Understanding GMDSS, 2012
As the term suggests, a satellite in polar orbit will travel its course over the geographical North and South Poles and will effectively follow a line of longitude. However, it must be remembered that the earth is revolving below the orbit and consequently the satellite will pass over any given point on the earth’s surface.
Monitoring pelagic Sargassum inundation potential for coastal communities
Published in Journal of Operational Oceanography, 2023
Joaquin Trinanes, N.F. Putman, G. Goni, C. Hu, M. Wang
Sensors with bands in the visible and near-infrared range, specifically between 550 and 1200 nm are good candidates for Sargassum detection. This is a requirement among other constraints related to the signal-to-noise ratio, and the spatial, spectral and radiometric resolutions. Data from the full set of bands contribute to the improvement of the quality of the final product, masking out the pixels contaminated by clouds, sun-glint, land or setting any other sensor-specific quality flags. The underlying data that contribute to the Experimental Weekly Sargassum Inundation Reports are based on satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua, and from the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi National Polar-orbiting Partnership (S-NPP). Each satellite views the entire Earth surface on a near-daily basis, collecting information in multiple bands (36 for MODIS, and 22 for VIIRS) at different spatial resolutions (250–500–1000 m MODIS, 375–750 m VIIRS). The sun-synchronous polar orbit guarantees that each pass takes place at similar solar times, providing consistent lighting.
Influence of observation angle change on satellite retrieval of aerosol optical depth
Published in Tellus B: Chemical and Physical Meteorology, 2021
Lijuan Chen, Ren Wang, Jiamei Han, Yong Zha
The Earth's near polar orbit satellite Terra was launched on December 18, 1999 as part of NASA's Earth Observing System (EOS) program. MISR has four bands including blue, green, red, and near-infrared, with central wavelengths of 446 nm, 558 nm, 672 nm, and 867 nm, respectively (Kahn et al., 2007). The nine observation cameras are An, Af, Aa, Bf, Ba, Cf, Ca, Df, Da (n, f, and a represent the nadir, forward, and backward, respectively; A, B, C, and D represent four lens designs whose focal lengths increase with increasing view angle, respectively (Da: −70.5°, Ca: −60.0°, Ba: −45.6°, Aa:-26.1°, An:0.0°, Af:26.1°, Bf: 45.6°, Cf: 60.0°, Df: 70.5°) (Diner et al., 1998; Martonchik et al., 2002). The nine angles are oriented along the direction of the satellite's flight path. In general, more oblique angles provide greater sensitivity to the effects of atmospheric aerosols. Clouds and medium angles are used for surface observations. In about seven minutes, all images of the nine angles at the same location can be acquired, the swath is 376 km for the nadir camera and 413 km for the other 8 cameras (Angal et al., 2016). The repeat period of the MISR image is 16 days, and its spatial resolution is 275 m and 1100 m (Table 1).
Satellite remote sensing of aerosol optical depth: advances, challenges, and perspectives
Published in Critical Reviews in Environmental Science and Technology, 2020
Xiaoli Wei, Ni-Bin Chang, Kaixu Bai, Wei Gao
Initially, the AOD products from satellites were only retrieved over dark target areas, such as over ocean or dense vegetation. The first AOD retrieval algorithm was developed for the AVHRR instrument (Stowe, Ignatov, & Singh, 1997, Stowe, Jacobowitz, Ohring, Knapp, & Nalli, 2002; Zhao et al., 2002) and the SeaWiFS detector (Sea-viewing Wide Field-of-view Sensor) onboard SeaStar (Hsu et al., 2012; Sayer et al., 2012a; 2012b). The land surface is complex due to its heterogeneity, high reflectance, instability, and anisotropic bidirectional characters. Hence, obtaining higher accuracy and a better description of the land surface reflectance is a great challenge for aerosol retrieval. Currently, with the development of satellite instruments, AOD algorithms can be divided into five categories for polar orbit satellites, including: 1) single-view spectral instruments methods, 2) multiple view-angle instruments methods (Kahn et al., 2005; Kokhanovsky et al., 2009), 3) polarization characteristic AOD retrieval algorithms, 4) retrieval AOD products using radar instruments, and 5) retrieval AOD products using a multisensor synergy method. The GOES sensors have a retrieval algorithm similar to a low earth orbit satellite, although some of them have their own retrieval algorithm for their own characters. Table 3 presents the detailed summary of the different AOD retrieval algorithms and the pros and cons of different satellites and sensors. They are introduced in detail below.