Rotational Raman scattering in the Earth's atmosphere ... - SRON

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116 Chapter 5 Figure 5.8: Same as Fig. 5.3, but for the spectral window combinations VIS + NIR and NUV + NIR.
Retrieval of cloud properties from NUV, VIS and NIR 117 suited to retrieve this cloud information for present and future GOME-type instruments. We compared the retrieval of cloud top pressure, cloud fraction, cloud optical thickness and surface albedo from three spectral windows that are currently used for this purpose: (1) the NUV window 350–400 nm, which contains pronounced Ring effect structures, (2) the VIS window 460–490 nm, which contains an O 2 -O 2 band, and (3) the NIR window 755–775 nm that contains the O 2 A band. Using the spectral windows separately we found that the VIS window provides the least information on cloud properties. The retrieval capability of this window is especially limited in the case of high and optically thick clouds. We found that the retrieval of cloud top pressure and cloud optical thickness from these measurements is very sensitive to random-like spectral biases on the reflectivity measurement. Since a significant amount of the cloud parameter information originates from the spectral continuum, the radiometric calibration limits the measurement interpretation. In all cases, the surface albedo in each window could only be retrieved for low cloud fractions. The NIR window is most capable of retrieving cloud top pressure. The strong O 2 A absorption feature in this window yields a high robustness to random-like biases. However, information on cloud optical thickness, which originates predominantly from the spectral continuum, is easily lost when random-like spectral biases increase. Another important aspect of the retrieval of cloud parameters from this window is that it is still possible to retrieve cloud top pressure with high retrieval sensitivity without using the spectral continuum, in contrast to the other windows. To a large extend this is also the case for the retrieval of cloud fraction. Thus, the NIR window allows one to retrieve cloud parameters even when the measurement is subject to large, spectrally broad calibration errors. Retrievals from NUV measurements show a retrieval sensitivity close to one for cloud fractions f c > 0.4 for all three cloud parameters but this information decreases rapidly for smaller cloud fractions. Furthermore, the retrieval from the NUV window is sensitive to random-like biases on the measurements. Nevertheless, even for a noise floor of 0.5% a reasonable performance is obtained. In this spectral window the cloud information is mainly extracted from the spectral continuum. Additionally, the Ring effect provides a small but significant contribution to the retrieval of cloud top pressure. When the relative spectral dependence of the continuum but not its absolute value is used cloud top pressure and cloud fraction can be retrieved adequately, but information is lost on cloud optical thickness. Due to the different performance of cloud retrieval from the NUV and NIR window a superior single window approach cannot be appointed. Both windows provide, to a certain extend, complementary information, which can be best exploited when both windows are used in a synergistic manner in a cloud retrieval as was proposed by van Diedenhoven et al. [2007]. Here the absolute continuum height and relative spectral dependence in the NUV window aid the retrieval of cloud fraction and cloud optical thickness, which are difficult to determine simultaneously from the NIR window continuum alone. We found that the Ring effect structures do not significantly contribute in this combination of the NUV and NIR window in terms of information content on cloud top pressure, cloud fraction, and cloud optical thickness. This means that for future instruments the requirement on the instrument spectral resolution of the NUV window to resolve the Ring effect structures can be relaxed for the purpose of cloud retrieval, because the Ring features do not have to be resolved when the NUV and NIR window are combined. Furthermore, this allows one to simplify the radiative transfer modeling
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VRIJE UNIVERSITEIT Rotational Raman
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Contents 1 Introduction 1 1.1 Obser
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1 Introduction 1.1 Observing skylig
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Introduction 3 Extracting the wealt
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Introduction 5 and Spurr, 1997, Vou
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Introduction 7 energy: E rot (v,J)
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Introduction 9 Figure 1.4: Probabil
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Introduction 11 scattered radiance
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Introduction 13 approximation in wh
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Introduction 15 scattering have bee
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2 A doubling-adding method to inclu
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A doubling-adding method to include
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40 Chapter 3 nm with a spectral res
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42 Chapter 3 contributions of lower
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44 Chapter 3 if we use the effectiv
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46 Chapter 3 This in turn results i
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48 Chapter 3 This may be shown in a
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50 Chapter 3 The forward and adjoin
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52 Chapter 3 Here, ∆ = diag [1, 1
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54 Chapter 3 Figure 3.3: Relative R
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56 Chapter 3 biases the simulation
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58 Chapter 3 3.4.2 Approximation me
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60 Chapter 3 where I ram,app and I
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62 Chapter 3 3.5 Simulation of pola
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64 Chapter 3 Figure 3.10: Relative
Page 72 and 73: 66 Chapter 3 dependence on the vert
Page 74 and 75: 68 Chapter 3 Figure 3.13: Same as F
Page 76 and 77: 70 Chapter 3 3.6 Summary A vector r
Page 78 and 79: 72 Chapter 3 where λ is the wavele
Page 80 and 81: 74 Chapter 3 where S l is the expan
Page 82 and 83: 76 Chapter 3 3.C Appendix: Evaluati
Page 85 and 86: 4 Accurate modeling of spectral fin
Page 87 and 88: Accurate modeling of spectral fine-
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Page 105 and 106: Retrieval of cloud properties from
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Page 125 and 126: References Aben, I., F. Helderman,
Page 127 and 128: References 121 Ellery, A., D. Wynn-
Page 129 and 130: References 123 Lacis, A. A., J. Cho
Page 131 and 132: References 125 Schulz, F., K. Stamn
Page 133 and 134: Summary A spectrum of sunlight that
Page 135 and 136: Summary 129 Earth radiance spectrum
Page 137 and 138: Samenvatting Het door de aardatmosf
Page 139 and 140: Samenvatting 133 met een vector-mod
Page 141: List of publications Peer-reviewed
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Rotational Raman scattering in the Earth's atmosphere ... - SRON

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