Errors in the remotely sensed ocean reflectance

An approximate method has been described to determine optical properties of the ocean surface from the reflected short-wave radiance at the top of the atmosphere. The non-scattered and singly scattered components of the radiation field have been taken into account exactly, the multiply scattered components - approximately. The calculations for a real atmospheric model have been compared with the results of an exact method for solving the radiation transfer equation.On the basis of the elaborated algorithm the sensitivity of the value of the remotely sensed spectral albedo of the ocean to the variations in optical thickness, single scattering albedo and aerosol phase function has been described as well as the influence of vertical inhomogeneity of the atmosphere.     

Validation of satellite-derived atmospheric temperature and water vapor concentration using radiosonde and rocketsonde measurements

Measurements of the spectral radiance of the earth's atmosphere from satellites can be related to the vertical structures of temperature and humidity. Derived profiles of these quantities are compared with radiosonde and rocketsonde observations, as well as with horizontal and vertical cross-sections of the atmosphere. In some regions of the atmosphere, particularly where large gradients are found, significant differences occur. A method for overcoming these by use of Typical Shape Functions is discussed. Transmittances computed from theory require modifications which are not well defined, and radiances measured from some satellite instruments disagree with computed values in ways which suggest calibration or instrument problems.     

Validation of SAGE II data inversions by the European correlative experiments

An European program of correlative experiments has been organized in order to validate SAGE II data during three periods of observation over Europe (November 1984, April 1985, October 1985). About ten groups from France, Belgium, Germany and Italy were participating. The correlative data are lidar aerosol profiles, soundings of ozone profiles, and balloon observations, including limb photographies, polarimetric measurements of the aerosol scattered light and nitrogen dioxide extinction measurements. Results of the comparisons between SAGE II inverted data and correlative data are presented. The analysis of the aerosol correlative observations with the SAGE II four aerosol channel data, in term of profile and size distribution is perfectly consistent and provide a good indirect validatioin. The NO₂ comparison shows a good agreement between SAGE II and correlative data.     

Retrieval of aerosol optical characteristics from polarization measurements of reflected solar radiation above the oceans

The reflected near infrared solar radiation observed from space above the oceans is due mainly to the atmosphere scattering, as the ocean surface is nearly black. The molecular Rayleigh contribution is also minimized at infrared wavelengths and it can be evaluated. It is shown that the degree of polarization is much more sensitive to the aerosol properties than the radiance. Measurements of polarization at two wavelengths and with an angular scanning are simulated and an inversion algorithm is proposed. It aims at finding an “equivalent aerosol model,” which reproduces the optical thickness and the asymmetry factor of the actual aerosol at all wavelengths in the solar spectrum.     

A method for estimating cross radiance

When imaging the surface from satellites or aircraft, “cross radiance” diminishes the information content of the pictures. In this paper a simple method is presented to estimate the value of cross radiance. This method includes a height-dependent aerosol size distribution model and the calculations refer to the single scattering approximation. The height variation of aerosol size distribution has significant effect on the value of cross radiance, while the areal distribution does not change much in comparison with that of the height-independent aerosol model.     

Voyager photopolarimeter observations of Saturn and Titan

The Voyager 2 photopolarimeter experiment observed the intensity and polarization of scattered sunlight from the atmospheres of Saturn and Titan in the near-UV at 2640 Å and in the near-IR at 7500 Å. Measurements of Saturn's limb brightening and polarization at several phase angles up to 70° indicate that a significant optical depth of UV absorbers are present in the top 100 mbar of Saturn's atmosphere in the Equatorial Zone and north polar region, and possibly at other latitudes as well. UV absorbers are prominent in polar regions, suggesting that charged particle precipitation from the magnetosphere may be important in their formation.The whole-body polarization of Titan is strongly positive in both the UV and near IR. If spherical particles are responsible for the polarization, no single size distribution or refractive index can account for the polarization at both wavelengths. The model atmosphere proposed by Tomasko and Smith [1], characterized by a gradient in particle size with altitude, seems capable of explaining the Voyager observations. If non-spherical particles predominate, the Voyager observations place important constraints on their scattering properties.     

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H₂SO₄ particles and of volcanic ash.     

The effect of aerosols on climate and aerosol climatology on the basis of observations from space

Principal aspects of the effect of aerosols on climate are discussed and the possibilities of obtaining a climatic data set of global aerosols are analyzed. Based on the analysis of space images, new data have been obtained on gigantic dust outbreaks in various regions of the Earth. It has been shown that dust outbreaks can propagate over hundreds and sometimes thousands of kilometers. The western Sahara - Atlantic Ocean is the major region of propagation of these outbreaks. The continent-to-continent trajectories of dust clouds have been discovered (from Africa to the coast of America, from Central Asia to the Pacific Ocean). Maps of the sources of strong dust transformations have been studied and drawn. In particular, an anthropogenic dust source has been found out on the northeastern coast of the Aral Sea. A striped mesostructure of dust formations has been analyzed, determined by both the inhomogeneous surface and peculiarities of the eddy dust transport. The techniques have been discussed in detail for retrieving the parameters of aerosol size distribution and the vertical profiles of the coefficients of aerosol extinction in the stratosphere and lower mesosphere from the data on the brightness of the twilight and daytime horizon as well as occultation measurements of solar radiation attenuation by the atmosphere.The difficulty of reliably predicting possible environmental changes arises both from the problems of estimating complex interactions of numerous processes and from a lack of information concerning various environmental parameters. For example, an important factor in present day climatic changes is the increased dust content of the atmosphere due to man's activities. However, a reliable estimate of this influence is found to be impossible due to the absence of definitive data on the global distribution of atmospheric dust and the properties of dust in various parts of the world [4,5,13–15]. The impact of aerosols on climate has been discussed in detail in a number of monographs [12–15].Observations from space have opened up new possibilities for studying atmospheric dust. For this purpose, both the imagery and spectrometry of the Earth's atmosphere from space are used. Rather attractive are the prospects for laser sounding [1].     

Solar-terrestrial research opportunities — A look to the future

In the late 1980's and in the 1990's we will have the opportunity to increase our knowledge of the sun, the heliosphere, and their influences on the earth's magnetosphere/ionosphere/atmosphere system. We should be able to gain increased knowledge of the physical mechanisms that drive the sun, the three-dimensional structure of the heliosphere, and the flow of energy and momentum from the sun through the interplanetary medium to the magentosphere/ionosphere/atmosphere system. We also may be able to evaluate the influence of the solar radiative output on the earth's atmosphere. Through well-coordinated national and international efforts we can plan and carry forward successful programs to accomplish these scientific goals. Space missions, ground-based observing networks, and rocket and balloon campaigns are needed and should be well-coordinated. Wide and easy access of data will help ensure the effectiveness of these programs. Retrospective studies, theory, modelling, simulations, and data analysis are also vital elements of research in this area. There are important scientific opportunities for scientists from all countries.     

Passive remote sensing of aerosols from space now and in the future

Aerosols modify scattered solar radiation leaving the atmosphere and this fact will be exploited to determine the aerosol optical depth. The interaction processes between solar radiation and aerosol particles are outlined. A quasi-linear relationship (‘conversion curves’) between the radiance at the satellite, L_sat, and the aerosol optical depth, a_Dλ, is found from both numerical and empirical studies. Because L_sat is not only controlled by a_Dλ, but also by a series of other atmospheric parameters (perturbing quantities), the concept of ‘favourable viewing conditions’ is presented, where the effects of the perturbing quantities are minimal. The paper ends with some lines of thought on a concept for a turbidity satellite.     

On the derivation of radiation budget parameters at the surface from satellite measurements

The modelling of climate and circulation processes requires more than ever before accurate data on the energy exchange between the earth's surface and the atmosphere. Accuracies are estimated to range between 2–20 Wm^?2 for global and monthly averages. The four components of the radiation budget at ground can still not at all be derived with sufficient accuracy from satellite measurements and from correlative data of conventional surface based origin. In this paper are discussed the general possibilities. Basic research is still required to establish a reliable error budget, and ground truth is essential.     

观测路径和光谱分辨率对吸收性气溶胶指数的影响

吸收性气溶胶指数（AAI）在监测污染物方面有较好的应用,其反演结果受边界层高度、云高、相对湿度以及仪器指标和观测几何路径等因素影响.利用大气辐射传输模型MODTRAN,对辐射传输方程中多次散射计算的不同近似方法和不同观测几何角度下的AAI进行模拟,研究这些因素对AAI结果的作用,并分析仪器光谱分辨率对AAI探测结果的影响.结果表明,折衷考虑计算效率与精度的情况下,应选择8流近似的离散坐标法进行带有多次散射计算的辐射方程解析.AAI在不同浓度和不同类型气溶胶下随观测角度变化的趋势相同:相对方位角<120°时,AAI误差在太阳天顶角和卫星方位角均为40°～60°时最大;相对方位角在120°～180°时误差均较小;光谱分辨率对AAI反演结果无明显影响.      

Boundary layer aerosol retrieval from thermal infrared nadir sounding – Preliminary results

A non-empirical algorithm is presented to retrieve the optical depth in the 750–1250 cm⁻¹ spectral range, of aerosol located in the boundary layer over the ocean, from nadir high-resolution radiance spectra in the thermal infrared. The algorithm is based on a line-by-line radiative transfer forward model and used the Optimal Estimation Method for the retrieval. Its performance strongly depends on the quality of the a priori temperature and H₂O atmospheric profiles. To demonstrate the relevance of the algorithm, distributions of maritime aerosol parameters have been retrieved from IMG/ADEOS data for December 1996, using the algorithm with the LBLRTM radiative transfer code, and ERA40 (ECMWF) a priori atmospheric profiles and surface conditions.     

Saturn's equatorial haze

We have measured the amount of Raman scattering in Saturn's equatorial zone and polar regions near the central meridian at the wavelengths of the H and K Ca II solar lines, 3934 Å and 3969 Å. Approximately 2.1% of the sunlight in this wavelength range is Raman scattered out of this range in Saturn's equatorial zone. Modeling the aerosol particle distribution as a clear, Rayleigh- and Raman-scattering gas over a dense haze yields an H₂ column abundance of about 40 km-Amagats. Comparison with results obtained by Pioneer 11 suggests that either the equatorial haze was 2.5 times deeper at the time of these observations (May, 1981) than at the time of the Pioneer 11 flyby (Sept., 1979); or the haze particles are much more strongly polarizing in blue light than they are in red light.     

SCIAMACHY limb measurements of NO2, BrO and OClO. Retrieval of vertical profiles: Algorithm,first results,sensitivity and comparison studies

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) measures scattered sun light also in limb viewing mode (i.e. tangential to Earth’s surface and its atmosphere), which allows determining vertical profiles of atmospheric trace gases. First results on the retrieval of NO₂, BrO and OClO profiles from the SCIAMACHY Limb measurements are presented and compared to independent satellite and balloon borne observations.     

Aerosol measurements from earth orbiting spacecraft

Since the fall of 1978, two Earth-orbiting spacecraft sensors, SAM II, for Stratospheric Aerosol Measurement II, and SAGE, for Stratospheric Aerosol and Gas Experiment have been monitoring the global stratospheric aerosol. These experiments use the Sun as a source to make Earth-limb extinction measurements during each spacecraft sunrise and sunset. This paper describes the global aerosol data base (climatology) that is evolving. Seasonal and hemispheric variations such as the springtime layer expansion with warming temperatures and the local wintertime polar stratospheric clouds (PSC's) will be described. The PSC's enhance extinction by up to two orders of magnitude and optical depths by as much as an order of magnitude over the background 1000 nm values of about 1.2 × 10^?4 km^?1 and 1.3 × 10^?3, respectively. The detection and tracking of a number of volcanoes whose effluents penetrated the tropopause are also described. The mass of new aerosol injected into the stratosphere from each volcano is estimated. The May 1980 eruption of Mount St. Helens, for example, produced about 0.32 × 10⁹ kg of new stratospheric aerosol enhancing the Northern Hemispheric aerosol by more than 100 percent.     

Mapping the earth's magnetic and gravity fields from space: Current status and future prospects

Orbital potential field measurements are sensitive to regional variations in earth density and magnetization that occur over scales of a few hundred kilometers or greater. Global field models currently available are able to distinguish gravity variations of ±5 milligal over distances of ～1,000 km and magnetic variations of ±6 gamma over distances of ～300 km at the earth's surface. Regional variations in field strength have been detected in orbital measurements that are not apparent in higher resolution, low altitude surveys. NASA is presently studying a spacecraft mission known as GRAVSAT/MAGSAT, which would be the first satellite mission to perform a simultaneous survey of the earth's gravity and magnetic fields at low orbital altitudes. GRAVSAT/MAGSAT has been proposed for launch during the latter nineteen-eighties, and it would measure gravity field strength to an accuracy of 1 milligal and magnetic field strength to an accuracy of 2 gamma (scalar)/5 gamma (vector components) over a distance of roughly 100 km. Even greater improvements in the accuracy and spatial resolution of orbital surveys are anticipated during the nineteen-nineties with the development of potential field gradiometers and a tethered satellite system that can be deployed from the Space Shuttle to altitudes of 120 km above the earth's surface.     

H2O concentration in the middle atmosphere: Processing of LIMS radiance measurements with a research algorithm

Transmittance functions as well as inversion algorithms have been developed for deriving H₂O profiles from radiometer measurements. These computer programs have been applied to evaluate own stratospheric balloon occultation measurements and LIMS (Limb Infrared Monitor of the Stratosphere) radiance measurements in the H₂O channel. The results are compared with the H₂O profiles in the LIMS data archive. The differences between corresponding H₂O profiles are discussed in dependence of altitude and latitude.     

Measurements of X-ray scattering from interstellar dust

We have examined the surface brightness profiles of four of the brightest compact galactic X-ray sources observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory for the existence of halos produced by the scattering of X-rays from interstellar dust. The sources are CYG X-3, 4U1658-48, GX13+1, and 4U1254-69. The halos are apparent when a comparison is made between each source's measured surface brightness profile and a model profile based upon a point response function (PRF) for each source. These model profiles depend upon knowledge of the source's spectrum, which is derived from the IPC itself and corroborated by the Einstein Monitor Proportional Counter and/or previous measurements.As conclusions rest entirely on a knowledge of the system (IPC and Mirror) PRF, we began this study with a comprehensive examination of the calibration data taken for the Observatory prior to launch. Point-source images for both the IPC and the HRI have been analyzed at various energies in order to gain a quantitative understanding of scattering by the mirror surface elements and the IPC's spatial resolution.All four sources show a significant excess above the response from a point-source. The attribution of the excess to X-rays scattered from interstellar dust is strengthened by the positive correlation of the magnitude of this excess with the observed column density of material along the line of sight. Furthermore, we have examined the surface brightness profiles of LMC X-1 and 3C273 and found them to have a greatly reduced excess above their model profiles. Because of their high galactic latitude and because only dust within our own galaxy will lead to the formation of a halo that extends beyond a few arcminutes, only a small effect is expected for these sources.