Photometric investigations a Introduction

Photometric measurements of planets and satellites often serve one of two distinct purposes. In the first case the local properties of surfaces or of clouds are sought. If this is accomplished for many places on a planet, then statements on the global characteristics can also be made. An instrument suitable for determination of local reflection properties requires a narrow field of view with many narrow-band channels at different wavelengths and a polarization measurement capability. Ideally,...

Mdp

1_I_I_____I_I__1200 400 600 800 WAVENUMBER (cm'1 Fig. 6.4.4 Top panel Iv(57.2 ), the average of 29 spectra near Titan's daytime east limb (average emission angle is 57.2 ). Bottom panel spectral limb function AI I Iv(57.2 ) - Iv(7.3 ) Iv(52.7 ), where Iv(7.3 ) is the average of 10 spectra near the center of the disk with an average emission angle of 7.3 (after Samuelson et al, 1981). 1_I_I_____I_I__1200 400 600 800 WAVENUMBER (cm'1 Fig. 6.4.4 Top panel Iv(57.2 ), the average of 29 spectra near...

Wwwwwwwwwwm

A ft A A a A A A A A A A ft A ft A A A A i i j vu v I1 i vvv ui'vvo vi iiy y v J '< IJ li V '.' V V i U V li 'J 'J lr V J I1 IJ Y ) V J 'J y1 -t C0s(2tirx) y2 - 2 cos (22 irx) y3 -1.5c0s(23ttx) y4 -0.5 C0S( 24 ir x ) y5 -0.8cos(25ttx> y6 -1.2 COs(26rx) y7 -1 c0s 27irx) y8 -1.6 cos 28 irx) y9 s -0.7 cos (29wx) y(0 - 1 cos(30ttx)

F n I Q

By definition, the phase function, I 0 1 0 , is unity at zero phase angle. For the outer planets a measurement of the phase integral cannot be performed from Earth, and data from a space platform are required. Considering Eq. 8.6.9 , 8.6.10 , and 8.6.17 , the geometric albedo is p p a,0 sina cos a dadfi. 8.6.19 For the special case of a Lambert surface, where p is a constant, p can be evaluated analytically, However, real surfaces and atmospheres deviate from the...

Instrument effects

Interpretation of planetary measurements is a difficult task, even when emission and reflection spectra are precisely known. In reality, the task is even more complicated because physical parameters of planetary atmospheres and surfaces must be retrieved from data recorded by real instruments. Such devices do not faithfully reproduce planetary spectra, such as the full resolution spectra discussed in Chapter 4. Instead, instruments modify the true spectral radiances in several ways. The...

The emerging radiation field

The last chapter dealt with the interaction of radiation with matter, mostly in the gaseous, but also in the liquid and solid phases. Absorption coefficients of infrared active gases, emission and scattering properties of surfaces, and single scattering albedos and phase functions of aerosols were considered. Applications of these concepts, along with the principles of radiative transfer discussed in Chapter 2, enable us to calculate the emerging radiation field of a planet or satellite. In...

B The solar radiation field

The solar flux crossing a horizontal plane depends on the Sun's elevation angle but is independent of azimuth. The infrared radiation field is always azimuthally symmetric. Therefore, because only fluxes contribute to heating rates, we are interested solely in azimuth-independent radiation fields in our analysis. By analogy with Eq. 2.5.10 , the appropriate equation for describing the transfer of radiation in the visible channel is a d v I tv, a - 2j2 amp IPi a PV I tv, aW - 4F amp IPi a Pi -ao...

Clouds and aerosols

The inference of cloud characteristics is based on much less sophisticated approaches than those for determining thermal structure and gas abundances. Clouds tend to be quite inhomogeneous compared with gaseous mixtures and require more parameters for adequate definition. Also, the appropriate equation of transfer Eq. 2.1.40 is considerably more complex than Eq. 8.2.1 , and not nearly as amenable to inversion techniques. Even so, direct techniques are sometimes capable of leading to rather...

Info

Fig. 6.3.2 Spectrum of Jupiter recorded with the Composite Infrared Spectrometer CIRS on Cassini. Fig. 6.3.2 Spectrum of Jupiter recorded with the Composite Infrared Spectrometer CIRS on Cassini. Fig. 6.3.3 Thermal emission spectra of Uranus and Neptune obtained with the Michelson interferometer IRIS carried on Voyager 2. The solid curves represent averages of 125 individual spectra from Uranus and 157 spectra from Neptune. For clarity the spectra have been offset from one another by 5 K. The...

Radiative equilibrium

The absorption of solar radiation leads to heating within the atmosphere, while cooling is achieved by the emission of infrared radiation. Thermal gradients are established, and the magnitudes and directions of these gradients, coupled with the forces of gravity and planetary rotation, give rise to imbalances in local pressure fields that lead to atmospheric motions. These internal motions are responsible for additional energy transport, and it is the balance of the dynamical and radiative...

Thermopile Detector

INTERFEROMETER MIRRORS AND BEAMSPLITTER ARE ROTATED 90 ABOUT AXIS INTERFEROMETER COLLECTOR 3.84 cm 01A Fig. 5.2.10 Optical layout of the infrared spectrometer on Voyager Hanel el al., 1980 . Fig. 5.2.11 Schematics of an off-axis Gregorian telescope, similar to one used on the Cosmic Background Explorer COBE Project, NASA . Fig. 5.2.11 Schematics of an off-axis Gregorian telescope, similar to one used on the Cosmic Background Explorer COBE Project, NASA . of the infrared photometer flown on the...

C Gas filter selective chopper and the pressure modulated radiometer

Besides solid substances infrared active gases may serve as filters. Many polyatomic gases have strong infrared absorption bands, each one consisting of numerous spectral lines. Absorption cells, charged with a suitable gas and hermetically sealed, are transparent, except at the narrow spectral intervals where the particular gas has absorption lines. Such filters are clearly not general purpose filters, but they are very useful for certain remote sensing tasks. The gas absorption cell differs...

B Chopped or ac radiometers

In the far infrared, where signals usually are weak and where detectors may show 1 f noise, operation at frequencies as low as a fraction of a hertz is often not possible for an explanation of 1 f noise see page 264. To raise the low frequency cut-off of such a radiometer is also undesirable. Inadequate reproduction of low frequencies affects mostly the overall signal level the absolute calibration , while inadequate response at high frequencies affects primarily spatial resolution and...