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since these cannot measure the quantity of interest, such as temperature, pressure, humidity etc., directly. By understanding emission and absorption processes, we can figure out what the instrument is looking at between the layers of atmosphere. While this type of instrument can also be operated
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that only detect what is already there. There can be a variety of sources for a passive instrument, including scattered radiation, light emitted directly from the sun, moon or stars—both more appropriate in the visual or ultra-violet range—as well light emitted from warm objects, which is more
627:. These can be generated either from models—e.g. state vectors from dynamical models and measurement vectors from radiative transfer or similar forward models—or from direct, empirical measurement. Other times when a statistical method might be more appropriate include highly
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instruments do not measure the relevant physical properties, that is the state, but rather the amount of radiation emitted in a particular direction, at a particular frequency. It is usually easy to go from the state space to the measurement space—for instance with
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looks at the edge of the atmosphere where it is visible above the Earth. It does this in one of two ways: either it tracks the sun, moon, a star, or another transmitting satellite through the limb as the source gets
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from ground stations or vehicles—optical methods can also be used inside in situ instruments—satellite instruments are particularly important because of their extensive, regular coverage. The
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Sensors that measure atmospheric constituents directly, such as thermometers, barometers, and humidity sensors, can be sent aloft on balloons, rockets or
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Sometimes the physics is too complicated to model accurately or the forward model too slow to be used effectively in the inverse method. In this case,
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behind the Earth, or it looks towards empty space, collecting radiation that is scattered from one of these sources. In contrast, a
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satellites, for instance, can sample the entire globe at better than one degree resolution in less than a day.
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concentration, pollution, and other properties. Such measurements are performed in a variety of ways including
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The following applies mainly to passive sensors, but has some applicability to active sensors.
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The more challenging case involves sensors, primarily satellite-mounted, such as
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Typically, there is a vector of values of the quantity to be retrieved,
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we can use some type of matrix inverse method—often the problem is
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Inverse
Methods for Atmospheric Sounding: Theory and Practice
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observation of atmospheres on different planets, such as the
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We can distinguish between two broad classes of sensor:
620:{\displaystyle \lbrace {\vec {x}}:{\vec {y}}\rbrace }
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663:Collocation (remote sensing)
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704:Clive D. Rodgers (2000).
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699:(2nd ed.). Wiley.
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172:instruments on three
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83:microwave radiometers
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678:Skew-T log-P diagram
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469:or of finding the
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422:empirically
163:as well as
149:radiometers
72:rocketsonde
33:temperature
25:atmospheric
689:References
631:problems.
536:regularize
431:Beer's law
211:occultated
187:, such as
161:ceilometer
123:dropsondes
64:radiosonde
45:wind shear
37:wind speed
629:nonlinear
609:→
594:→
528:ill-posed
497:−
490:→
454:→
439:inverting
405:→
370:→
355:→
340:→
302:→
269:→
223:SCIAMACHY
741:Category
657:See also
532:unstable
178:EUMETSAT
176:and two
79:infrared
29:pressure
193:passive
109:on the
57:in situ
524:linear
231:zenith
185:active
219:nadir
189:radar
165:sodar
157:lidar
153:radar
49:ozone
174:NOAA
170:AMSU
159:and
141:and
101:AMSU
99:and
97:AIRS
81:and
55:and
39:and
557:or
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19:or
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