Study On Retrieval Of Atmospheric Trace Gas Concentration From Saatellite Based Limb Radiance

The atmospheric trace gases are atmospheric constituents of great importance. They are involved in the biogeochemical cycle by the effect of physics, chemistry, biology, and the earth process. The atmospheric trace gases play major role in the evolution of life on earth, atmospheric chemistry development, and the change of the global environment. Ozone is able to protect biological organisms from harmful solar ultraviolet radiation that has the potential of damaging organic macromolecules vital to life. Evolution of life on land is thought to have become possible because of ozone formation through oxygenic photosynthesis. The photolysis cycle of ozone has some important implications for the vertical structure of the Earth's atmospheric temperature. Furthermore, ozone is a tracer for environmental pollution caused by human activities. NO2 is of great importance in the catalytic destruction of ozone in the stratosphere, and it will result in great impacts to global atmospheric and ecologic environment, such as photochemical smog, acid rain, greenhouse effect. With the huge increase of the density of atmospheric NO2 led by the recently rapid development of industry, NO2 has become one of the most important indicators of the atmospheric pollution. From 1980s, the discovery of the ozone hole of the Antarctic pole and the increasing air pollution of the photochemical smog in the city promote the investigation of atmospheric trace gases and local environmental pollution. Consequently, the research on temporal and spatial distribution of atmospheric trace gases have recently been one of the front and focused issues.The observation of atmospheric trace gases has been studied from the ground, balloons, rocket, and the current satellite. In comparison with ground based spectrometer and the sonde aboard the balloon or rocket, the satellite based instrument, which traditionally involves nadir and occultation mode, is capable of observing the ozone and other trace gases at a higher spatial resolution with a significantly better global coverage. The nadir technique is capable of producing global maps of the total trace gas column with a high spatial resolution, but the retrieved profiles have very limited vertical resolution. The occultation technique can provide density profiles of trace gas with high vertical resolution, but it suffers from poor geographical coverage.In recent years, a new technique has been developed that measures the atmospheric limb scattered radiance at series tangent altitudes, which has been first applied in Solar Mesosphere Explorer (SME) by NASA (National Aeronautics and Space Administration) in 1981. This technique, combining the advantages of other techniques, provides vertical profiles of trace gas with high vertical resolution comparable to that of occultation measurements and with significantly better global coverage as nadir observations. One of the instruments is SCanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) aboard the European Space Agency (ESA)'S ENVIronment SATellite (ENVISAT), launched on March 1,2002. The SCIAMACHY scans an area lying 3280 km ahead at the horizon in flight direction, from earth surface to about 92 km with a vertical step of about 3.3 km. The SCIAMACHY observes limb radiance in the wavelength range from the ultraviolet (214 nm) to the near infrared (2386 nm) with moderate resolution (0.24-1.48 nm). Another satellite instrument capable of limb observation is Optical Spectrograph and InfraRed Imaging system (OSIRIS) aboard Odin satellite, launched on February 20,2001. The OSIRIS consists of optical spectrograph (OS) and infrared imaging system (IRI), two dependent instruments. The OS and IRI measures UV-VIS limb scattered radiance between 7 and 70 km and limb airglow radiance in Oxygen InfraRed Atmospheric (OIRA) bands from 7 to 100 km with a vertical step of 2 km respectively. A number of studies on retrieval of vertical profiles of atmospheric trace gases have been carried out from limb scattered radiance, such as SCIAMACHY and OSIRIS measurements. Commonly, the wavelength pairing method or Differential Optical Absorption Spectroscopy (DOAS) technique is applied to limb radiance to obtain the retrieval vector or effective column abundances, from which the trace gas profiles are retrieved by optimal estimation limited in the stratosphere altitude ranges.In this thesis, a novel retrieval strategy, wavelength paring method coupling with Weighted Multiplicative Algebraic Reconstruction Technique (WMART), in which a forward model SCIATRAN (radiative TRANsfer model for SCIAMACHY) embeds, is employed to retrieve the profiles of trace gas from limb scattered radiance. Examples are presented using the SCIAMACHY limb measurements for the retrieval of vertical number density profiles of ozone and NO2. First, the limb radiance profiles are normalized with respect to a reference tangent altitude, and then the normalized radiances are combined to produce the retrieval vector, at last, the number density profiles are recovered using the WMART algorithm. A program package SCIA_JLU for batch retrieving ozone and NO2 profiles from SCIAMACHY LIB limb data has been developed, and it will cost 30 min and 15 min roughly for ozone and NO2 profiles retrieval from one orbit data respectively. It has reduced one order of magnitude of the impact of uncertain parameters, such as cloud, albedo, and aerosol, on radiance after wavelength pairing, but the sensitivity of radiance to retrieving trace gas has kept. The wavelengths suited to ozone and NO2 profiles retrieval are determined according to the features of limb radiance profile, weighting function of radiance, and weighting function of retrieval vector for ozone and NO2. The best wavelengths for ozone are in ozone Hartley bans in which the wavelengths 267.5 nm,286.5 nm,287.5 nm and 305.1 nm are paired with a weaker absorption wavelength 307.5 nm respectively, and Chappuis bands in which a triplet consisting of a strongly absorption wavelength 599 nm combined with the other two weaker absorbing wavelengths 525 nm and 668 nm on either side. Accordingly, the retrieval altitude region for ozone are decided, i.e.10-68 km. Three optimal wavelengths triplet combined similar to ozone Chappuis bands in the spectra range from 420 to 450 nm are chosen for NO2 retrieving and the corresponding retrieval altitude region is between 15 and 40 km. Furthermore, the weighting factor for each pair or triplet and for each tangent altitude for trace gas profile retrieving at every altitude are determined. The stratospheric and mesospheric number density profiles of ozone are retrieved and combined using SCIAMACHY limb radiance in ozone Hartley and Chappuis absorption bands, by the proposed scheme combined WMART and SCIATRAN which is applied to SCIAMACHY limb measurements. The stratospheric vertical profiles of NO2 are also derived from SCIAMACHY limb radiance in the wavelengths range between 435 and 451 nm by the technique just as the ozone retrieving method.A comprehensive sensitivity study is presented which investigate the error of the retrieved profiles introduced by incorrect or insufficient knowledge of uncertain parameters. The incorrect retrieved profiles caused by the major error sources, such as tangent altitude pointing, boundary layer visibility, stratospheric aerosol loading, aerosol extinction coefficient, surface albedo, cloud height, as well as cloud optical depth, compare with the assumed "correct" retrieved profiles to obtain the relative percent difference between them. The results suggest that, a total error due to the tangent altitude pointing bias achieves maximum, followed by the error result from insufficient aerosol parameters, and the error led by incorrect surface albedo and cloud is minimum, when the parameters are in their perfect accuracy. Whereas, in the stratosphere, the effect of aerosol parameters bias is higher than that of pointing bias, because of the huge error result from the presence of vocalic aerosol, i.e., like the error of retrieved ozone will approach as greater as 42% , even the error of retrieved NO2 will be beyond 100% at the altitude of 15 km. What's more, the error of both ozone and NO2 decreases with the increasing altitude generally, while the error led by only surface albedo and cloud depends on the solar zenith angle. The results also show that the errors of NO2 are greater than those of ozone caused by the same incorrect parameters.In order to evaluate this inversion strategy, the retrieved ozone profiles have been validated with SCIAMACHY ozone V2.3 provided by University of Bremen (so-called BU ozone), OSIRIS ozone V3.0 provided by University of Saskatchewan, and Microwave Limb Spectrometer (MLS) ozone, while the retrieved NO2 profiles have been validated with SCIAMACHY NO2 V3.1 provided by University of Bremen (BU NO2) and OSIRIS NO2 V3.0 provided by University of Saskatchewan. The coincidences between retrieved profiles and BU profiles are in the same location and time during 3 days due to retrieval from the same source data, while the other coincidences also occurs during 3 days and meet the coincidence criteria which are±5°latitude,±10°longitude. Generally, there is best agreement between the retrieved and BU ozone profiles, while the differences are within 15% , while the maximal difference between the retrieved and OSIRIS ozone is up to 20% , and the agreement between the retrieved and MLS ozone is the worst, while the difference is less than 10% only between 20 and 46 km. For NO2, between 15 and 40 km, the retrieved and BU profiles agree within 10% , and the difference between retrieved and OSIRIS profiles is up to about 16% while within 10% for most altitudes.Another retrieval of two dimensional (2D) profiles of mesospheric ozone has been investigated from OSIRIS limb airglow radiance at 1.27μm. First, the 2D profiles of Volume Emission Rate (VER) are derived from the limb airglow radiance observed by IRI, by the developed effective tomographic technique suitable for satellite application in limb geometry; then the ozone profiles between 50 and 90 km are retrieved from the VER profiles based on both the onion peeling method and Newton iteration method coupling with odd oxygen photochemical model which connected ozone and VER quantitatively. Note that this photochemical model has been illustrated to be reliable through the comparison between the VER profiles modeled by this model and retrieved from IRI limb airglow radiance. The ozone profiles decrease exponentially with the increasing altitude; however, the second peek near 80 km hasn't been identified evidently. From the comparison of selected ozone vertical profiles between retrieved and BU, the differences by Newton iteration are less than onion peeling method whose mean difference are within 12% and are almost 10% except for several altitudes.At last, a novel satellite based limb scatter observing with a new retrieving technique is proposed based on the work of mesospheric ozone retrieving. This new technique, which combines the differential optical absorption spectroscopy (DOAS) method and tomographic retrieving algorithm, is able to recover the 2D trace gas profiles from ultraviolet-visible limb scattered radiance. The requirement for this technique is presented, and the two steps including retrieving of column abundances through DO AS analyzing on limb radiance and the retrieving of trace gas profiles by tomography from column abundances has been described in detail. The test retrieval of NO2 profiles shows that there is a good agreement in both structure and magnitude between the retrieved and input test profiles excluding the great edged errors, while the differences are within 15% between 25 and 65 km, and even less within 5% below 40 km.It is concluded that the novel wavelength paring and WMART coupling with SCIATRAN strategy present a powerful and reliable technique to retrieve trace gas profiles with high accuracy, high vertical resolution, optimal speed, extent altitude region on a global scale, from satellite based limb scattered measurements made with high performance spectrometers. The mesospheric ozone can be recovered from limb airglow radiance by tomography, furthermore, the proposed technique based on the investigation of mesospheric ozone retrieval, which combines DOAS and tomography provides a new possible method for the retrieval of trace gas that allows for the 2D structure.