Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

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.     

The new ESA meteoroid model

The orbital distributions of meteoroids in interplanetary space are revised in the ESA meteoroid model to account for recently obtained observational data and to comply with the constraints due to the orbital evolution under planetary gravity and Poynting–Robertson effects. Infrared observations of the zodiacal cloud by the COBE DIRBE instrument, in situ flux measurements by the dust detectors on board Galileo and Ulysses spacecraft, and the crater size distributions on lunar rock samples retrieved by the Apollo missions are synthesized into a single model. Within the model, the orbital distributions are expanded into a sum of contributions due to a number of known sources, including the asteroid belt with the emphasis on the prominent families Themis, Koronis, Eos and Veritas, as well as comets on Jupiter-encountering orbits. An attempt to incorporate the meteor orbit database acquired by the AMOR radar is also discussed.     

A comparison of atmospheric aerosol measurements by various satellite sensors

Investigations to measure the vertical optical thickness of aerosols over ocean surfaces has been conducted using several different satellite sensors. Landsat 1 and Landsat 2 data originally confirmed that a linear relationship exists between the upwelling visible radiance and the aerosol optical thickness (about 90% of this thickness is generally in the lowest 3 km of the atmosphere). Similar relationships have also been found for sensors on GOES-1, SMS-2, NOAA-5, and NOAA-6 satellites. The linear relationship has been shown theoretically to vary with the aerosol properties, such as size distribution and refractive index, although the Landsat data obtained at San Diego showed little variability in the relationship. The differences between the results found for the various satellite sensors are discussed, and are attributed mainly to uncertainties in the calibration of the sensors. To investigate the general applicability of the technique to different locations, a global-scale ground truth experiment was conducted with the AVHRR sensor on NOAA-6 to determine the relationship at eleven ocean sites around the globe. Analysis of the data shows good agreement between the satellite and ground truth values of the aerosol optical thickness, and indicates that the technique has global application. At two of the sites, multispectral radiometric measurements of the Junge aerosol size distribution parameter were made, and showed good agreement with a value inferred from the AVHRR Channels 1 and 2 radiances.     

Satellite stratospheric aerosol measurement validation

The validity of the stratospheric aerosol measurements made by the satellite sensors SAM II and SAGE has been tested by comparing their results with each other and with results obtained by other techniques (lidar, dustsonde, filter, impactor). The latter type of comparison has required the development of special techniques that (1) convert the quantity measured by the correlative sensor (e.g. particle backscatter, number, or mass) to that measured by the satellite sensor (extinction), and (2) quantitatively estimate the uncertainty in the conversion process. The results of both types of comparisons show agreement within the measurement and conversion uncertainties. Moreover, the satellite uncertainty is small compared to aerosol natural variability (caused by seasonal changes, volcanoes, sudden warmings, vortex structure, etc.). Hence, we conclude that the satellite measurements are valid.     

Can turbidity measurements be used for the estimation of aerosol parameters?

In a previous paper the authors showed that the aerosol size distribution can be estimated with reasonable accuracy from spectral extinction measurements in a limited spectral region (λ ≤ 1 μm) only. Using the same method it will be discussed if the anticipated WMO turbidity network with four spectral channels has the potential of estimating the aerosol size distribution.     

A surface reflectance correction model to improve the retrieval of MISR aerosol optical depth supported by MODIS data

Combined use of different satellite sensors are known to improve retrievals of aerosol optical depth (AOD). In this study, we propose a new method for retrieving Multi-angle Imaging SpectroRadiometer (MISR) AOD data supported by Moderate Resolution Imaging Spectroradiometer (MODIS) data in Jiangsu Province, China, over the period of 2016–2018 using MODIS L1B, bidirectional reflectance distribution function (BRDF), MISR 1B2T, and ground-measured AOD data. This method is based on the surface reflectance determined by the MODIS V5.2 algorithm. Through the observation angle and spectral conversion between different sensors, the MISR AOD can be obtained. The correlation coefficient (R) and root-mean-square error (RMSE) between the retrieved MISR and ground-measured AOD data varied between different seasons. The accuracy of the MISR AOD retrieval was notably improved after correcting the MISR surface reflectance. Therefore, the method proposed in this study is feasible for the retrieval of MISR AOD supported by MODIS data, and will be applicable to atmospheric environmental monitoring over large areas in the future.     

Intercomparisons of temperature,density and wind measurements from in situ and satellite techniques

Intercomparisons between satellite retrieved temperatures (TIROS N series) and those derived from radiosonde and rocketsonde profiles have been made covering the years 1980–1984. Differences in the measurement parameters between 100 and 0.4 mbar (～16–55 km) are described; generally radiosonde/satellite differences are less than 1°K, while rocketsonde/satellite differences reach 7–8°K in the upper stratosphere. Comparisons between the various $\text{in situ}$ devices indicate that radiosonde/rocketsonde differrences are less than 1°K while precision studies of the rocketsonde instrument find that the rocketsonde measurements are internally consistent to less than 1°K up to 50 km and to less than 3°K to 60 km. Density data obtained with the small rocketsondes ($\text{in situ}$ thermistors and inflatable spheres) and with the large sounding rocket systems show that density measurements usually agree to within 15 percent up to 85 km. Comparisons of the various atmospheric parameters obtained from different instruments are important, however the usefulness of intermixing the measurements is obvious and increased emphasis should be placed on procedures for intermingling such data. Suggestions are made on how this might be accomplished.     

Evaluation and utilization of CloudSat and CALIPSO data to analyze the impact of dust aerosol on the microphysical properties of cirrus over the Tibetan Plateau

The present study elucidates on the evaluation of two versions (V3 and V4.10) of vertical feature mask (VFM) and aerosol sub-types data derived from the Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations (CALIPSO), and its utilization to analyze the impact of dust aerosol on the microphysical properties of cirrus over the Tibetan Plateau (TP). In conjunction to the CALIPSO, we have also used the CloudSat data to study the same during the summer season for the years 2007–2010 over the study area 25–40°N and 75–100°E. Compared to V3 of CALIPSO, V4.10 was found to have undergone substantial changes in the code, algorithm, and data products. Intercomparison of both versions of data products in the selected grid between 30–31°N and 83–84°E within the study area during 2007–2017 revealed that the VFM and aerosol sub-types are in good agreement of ～95.27% and ～82.80%, respectively. Dusty cirrus is defined as the clouds mixed with dust aerosols or existing in dust aerosol conditions, while the pure cirrus is that in a dust-free environment. The obtained results illustrated that the various microphysical properties of cirrus, namely ice water content (IWC), ice water path (IWP), ice distribution width (IDW), ice effective radius (IER), and ice number concentration (INC) noticed a decrease of 17%, 18%, 4%, 19%, and 10%, respectively due to the existence of dust aerosol, consistent with the classical “Twomey effect” for liquid clouds. Moreover, the aerosol optical depth (AOD) showed moderate negative correlations between ?0.4 and ?0.6 with the microphysical characteristics of cirrus. As our future studies, in addition to the present work undertaken, we planned to gain knowledge and interested to explore the impact of a variety of aerosols apart from the dust aerosol on the microphysical properties of cirrus in different regions of China.     

An update global model of hmF2 from values estimated from ionosonde and COSMIC/FORMOSAT-3 radio occultation

In this paper, we present our recent work on developing an updated global model of the ionospheric F2 peak height hmF2 parameter by combining data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC/FORMOSAT-3) radio occultation (RO) measurements and from the extended global ionosonde stations. In particular, 10 Chinese ionosonde stations’ data are newly introduced into this study. The modeling technique used is based on a two-layer empirical orthogonal function (EOF) expansion. Global distributions of hmF2 maps calculated using the newly constructed global model and the one provided by the International Reference Ionosphere model (IRI-ITU-R) are compared with the global distributions of hmF2 obtained by the COSMIC RO measurements and quantitative statistical analysis of the differences between the model results and those of the COSMIC RO measurements is made for the low (2008) and high (2012) solar activity years. The obtained average root-mean-square differences (RMSEs) for our model are 27.7 km (11.1%) and 31.0 km (9.8%), respectively for the years 2008 and 2012, whereas those for the IRI-ITU-R model are 39.9 km (16.9%) and 35.0 km (11.6%), respectively. Comparison of the results calculated both by our model and the IRI-ITU-R model with the digisonde observation is also made. The comparisons show that the newly constructed global hmF2 model can reproduce reasonably well the observations and perform better than IRI-ITU-R model.     

Latitude gradients in the natural variance in stratospheric conductivity – Implications for studies of long-term changes

Stratospheric electrical conductivity measurements have been made from high altitude research balloons at various locations around the world for more than 40 years. In the stratosphere, conductivity changes may indicate changes in aerosol or water vapor content. In this paper, we will compare the short term variation amplitude in data taken at several latitudes from equatorial to polar cap. Short term variations that occur on time scales of weeks to months (10⁵–10⁷ s) can be attributed to Forbush decreases, geomagnetic storms, aerosol injections by volcanos and forest fires, etc. Variations with time scales of minutes to days (10³–10⁵ s) can have amplitudes of a factor of ∼2 or more at high magnetic latitude. The variance at equatorial latitude is much smaller. The sources of these fluctuations and the latitude gradient remain unknown. Variations of all origins completely obscure any long-term climatic trend in the data taken in the previous four decades at both mid and high latitude.     

Spectral and temporal characteristics of aerosol optical depth over a wet tropical location in North East India

A network of multi wavelength solar radiometer (MWR) stations has been in operation since the 1980s in India for measurement of aerosol optical depth (AOD). This network was augmented recently with the addition of a large number of stations located across the length and breath of India covering a variety of climate regimes. The spectral and temporal variations of aerosol optical depths observed over Dibrugarh located in the North East of India (27.3°N, 94.5°E) are investigated by analyzing the data obtained from a MWR during October 2001–September 2003 using the Langley technique. AOD varies with time of the day, month of the year and season. From January to April and October to December, aerosol optical depth decreases with wavelength whereas during May–September aerosol optical depth has been found to be nearly independent of wavelengths. AOD is higher during pre-monsoon season (March–May) and lower in the monsoon (June–September) season at about all wavelengths. The temporal variation of AOD over Dibrugarh have also been compared with those reported from selected locations in India.     

铝基微结构光栅几何参数反演

微结构光栅是一种广泛应用的电子元件。采用随机微粒群优化(SPSO)算法反演了一维铝基衬底矩形光栅的几何结构参数。首先介绍了严格耦合波分析(RCWA)法和微粒群优化算法的基本原理,并采用RCWA法求解了光栅内电磁场问题;然后根据正问题求得的光栅光谱反射率建立目标函数,并采用SPSO算法优化目标函数,反演得到单槽和双槽矩形光栅的周期、凸脊宽度和凹槽深度;最后分析了种群大小和搜索区间对反演结果的影响。结果表明,SPSO算法可以准确地反演光栅几何结构参数,并推荐种群数取30。     

Impact of emissions from anthropogenic sources on satellite-derived reflectance

The present study deals with the impact of extensive anthropogenic activities associated with festivities and agricultural crop residues burning in the Indo-Gangetic Plains (IGP) on satellite-derived reflectance during November 2007. Intense smoke plumes were observed in the IRS-P4 OCM satellite data over IGP associated with agricultural crop residue burning during the study period. Terra-MODIS AOD and CALIPSO LIDAR backscatter datasets were analysed over the region to understand the spatial and temporal variation of the aerosol properties. Ground-based measurements on aerosol optical properties and black carbon (BC) mass concentration were carried out during 7–14 November 2007 over urban region of Hyderabad, India. Top of the Atmosphere (TOA) reflectance estimated from IRS-P4 Ocean Color Monitor (OCM) data showed large variations due to anthropogenic activities associated with crop residue burning and fireworks. Atmospheric corrections to OCM satellite data using 6S radiative transfer code with inputs from ground and satellite measurements could account for the variations due to differential aerosol loading. Results are discussed in this paper.     

Spaceborne lidar measurement accuracy: Simulation of aerosol,cloud, molecular density,and temperature retrievals

Spaceborne lidar measurements and retrievals are simulated using realistic errors in signal, conventional density information, atmospheric transmission, and lidar calibration. We find that by day, independent analysis of returns at wavelengths of 0.53 and 1.06 μm yields vertical profiles (0.1- to 1-km resolution) of tenuous clouds and boundary-layer, Saharan, and strong volcanic stratospheric aerosols to accuracies of 30% or better, provided particulate optical depth does not exceed ?0.3. By night all these constituents are retrieved, plus noctilucent clouds, mesospheric aerosols, and upper tropospheric/nonvolcanic stratospheric (UT/NVS) areosols. Molecular-density uncertainties are a dominant source of error for UT/NVS retrievals.To reduce these errors and also to provide density and temperature profiles, we developed a procedure that combines returns at 0.35 and 1.06 μm. This technique significantly improves UT/NVS aerosol retrieval accuracy and also yields useful density and temperature profiles there. Strong particulate contamination limits the technique to the cloud-free upper troposphere and above.     

Remote sensing of aerosol and radiation from geostationary satellites

The paper presents a high-level overview of current and future remote sensing of aerosol and shortwave radiation budget carried out at the US National Oceanic and Atmospheric Administration (NOAA) from the US Geostationary Operational Environmental Satellite (GOES) series. The retrievals from the current GOES imagers are based on physical principles. Aerosol and radiation are estimated in separate processing from the comparison of satellite-observed reflectances derived from a single visible channel with those calculated from detailed radiative transfer. The radiative transfer calculation accounts for multiple scattering by molecules, aerosol and cloud and absorption by the major atmospheric gases. The retrievals are performed operationally every 30 min for aerosol and every hour for radiation for pixel sizes of 4-km (aerosol) and 15- to 50-km (radiation). Both retrievals estimate the surface reflectance as a byproduct from the time composite of clear visible reflectances assuming fixed values of the aerosol optical depth. With the launch of GOES-R NOAA will begin a new era of geostationary remote sensing. The Advanced Baseline Imager (ABI) onboard GOES-R will offer capabilities for aerosol remote sensing similar to those currently provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) flown on the NASA Earth Observing System (EOS) satellites. The ABI aerosol algorithm currently under development uses a multi-channel approach to estimate the aerosol optical depth and aerosol model simultaneously, both over water and land. Its design is strongly inspired by the MODIS aerosol algorithm. The ABI shortwave radiation budget algorithm is based on the successful GOES Surface and Insolation Product system of NOAA and the NASA Clouds and the Earth’s Radiant Energy System (CERES), Surface and Atmospheric Radiation Budget (SARB) algorithm. In all phases of the development, the algorithms are tested with proxy data generated from existing satellite observations and forward simulations. Final assessment of the performance will be made after the launch of GOES-R scheduled in 2012.     

Remote monitoring of aerosols from space

Using the four-channel teleradiometer “Micron” aboard the Orbital Stations “Salyut-4” and “Salyut-6” the brightness profiles were determined in the near-infrared spectral region up to the height of 60 km (in case of noctilucent clouds up to 80–85 km). Proceeding from the data above we obtained information on the global and vertical distributions of atmospheric aerosol, water vapour concentration and the optical properties of the noctilucent clouds.     

Detection of aerosol pollution sources during sandstorms in Northwestern China using remote sensed and model simulated data

The present paper has used a comprehensive approach to study atmosphere pollution sources including the study of vertical distribution characteristics, the epicenters of occurrence and transport of atmospheric aerosol in North-West China under intensive dust storm registered in all cities of the region in April 2014. To achieve this goal, the remote sensing data using Moderate Resolution Imaging Spectroradiometer satellite (MODIS) as well as model-simulated data, were used, which facilitate tracking the sources, routes, and spatial extent of dust storms. The results of the study have shown strong territory pollution with aerosol during sandstorm. According to ground-based air quality monitoring stations data, concentrations of PM₁₀ and PM_2.5 exceeded 400?μg/m³ and 150?μg/m³, respectively, the ratio PM_2.5/PM₁₀ being within the range of 0.123–0.661. According to MODIS/Terra Collection 6 Level-2 aerosol products data and the Deep Blue algorithm data, the aerosol optical depth (AOD) at 550?nm in the pollution epicenter was within 0.75–1. The vertical distribution of aerosols indicates that the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) 532?nm total attenuates backscatter coefficient ranges from 0.01 to 0.0001?km^?1?×?sr^?1 with the distribution of the main types of aerosols in the troposphere of the region within 0–12.5?km, where the most severe aerosol contamination is observed in the lower troposphere (at 3–6?km). According to satellite sounding and model-simulated data, the sources of pollution are the deserted regions of Northern and Northwestern China.     

Satellite measurements of tropospheric aerosols

The ability to measure tropospheric aerosols over ocean surfaces has been demonstrated using several different satellite sensors. Landsat data originally showed that a linear relationship exists between the upwelling visible radiance and the aerosol optical thickness (about 90% of this thickness is generally in the lowest 3 km of the atmosphere). Similar relationships have also been found for sensors on GOES, NOAA-5 and NOAA-6 satellites. The linear relationship has been shown theoretically to vary with the aerosol properties, such as size distribution and refractive index, although the Landsat data obtained at San Diego showed little variability in the relationship. To investigate the general applicability of the technique to different locations, a global-scale ground-truth experiment was conducted in 1980 with the AVHRR sensor on NOAA-6 to determine the relationship at ten ocean sites around the globe. The data for four sites have been analyzed, and show excellent agreement between the aerosol content measured by the AVHRR and by sunphotometers at San Diego, Sable Island and San Juan, but at Barbados, the AVHRR appears to overestimate the aerosol content. The reason for the different relationship at the Barbados site has not been definitely established, but is most likely related to problems in interpreting the sunphotometer data rather than to a real overestimation by the AVHRR. A preliminary analysis of AVHRR Channel 1 (0.65 μm) and Channel 2 (0.85 μm) radiances suggest that useful information on the aerosol size distribution may also be obtained from satellite observations.