Solar Backscatter Ultraviolet Research Articles

Ozone Variations Derived by a Chemical Transport Model

The results of a comparison between monthly mean ozone column variations calculated from the chemical transport model Oslo CTM2 and those derived from solar backscatter ultraviolet (SBUV) satellite observations are presented for the period 1998-2009. Monthly mean total ozone derived from improved model simulations were used to com- pute monthly zonal means over 10° latitude zones over the northern and southern hemispheres. Ozone column variations from Oslo CTM2 are highly corre- lated with SBUV retrievals at all latitude zones. Equa- torial zonal winds at 30 hPa were used as index to study the impact of quasi-biennial oscillation (QBO) on ozone. Correlations between modeled ozone and the QBO were found to be the order of +0.8 in the tropics. The impact of QBO was most pronounced at equatorial latitudes with amplitudes of +4 to � 4% . Seasonal variations in surface ozone and tropospheric ozone column calculated by the model are also presented.

紫外臭氧垂直探测仪高精度在轨光谱定标方法研究

紫外臭氧垂直探测仪高精度在轨光谱定标方法研究

Radiometric Calibration of the Solar Backscatter Ultraviolet Sounder and Validation of Ozone Profile Retrievals

The Solar Backscatter Ultraviolet Sounder (SBUS) is one of the 11 main payload instruments onboard Feng Yun-3 (FY-3), the second generation of Chinese polar orbit meteorological satellites. This paper presents the results of SBUS instrument calibration, and data and product validation during the prelaunch and postlaunch periods. Topics include the instrument prelaunch calibration and characterization, in-orbit monitoring, validation of the ozone profiles retrieved from the FY-3 SBUS measurements, and an application of the retrievals to monitoring the 2011 Arctic ozone depletion. For the prelaunch calibration of SBUS, the estimated uncertainty of laboratory calibration is approximately 4.7%. The in-orbit solar irradiance measurements indicate that the diffuser reflectivity degraded approximately 15% for the 252-nm channel, and 3% to 5% for the other 11 channels during a 12-mo period. Using ozone vertical profiles retrieved from National Oceanic and Atmospheric Administration Solar Backscatter Ultraviolet (SBUV)/2s as a “truth,” the initial comparison of ozone profiles between FY-3 SBUS and SBUV/2s finds that the relative percent bias of the FY-3 SBUS with the SBUV/2 results is good. The averaged differences range over to ±7% for FY-3A SBUS and ±6% for FY-3B SBUS. The SBUS ozone profile retrievals reveal that the spring 2011 Arctic ozone depletion mainly resulted from a sharp ozone decrease in the upper troposphere to lower stratosphere, which accounts for 70% to 80% of the total ozone loss.

Validation of total ozone data between satellite and ground-based measurements at Zhongshan and Syowa stations in Antarctica

We present validation between total ozone from satellite and ground-based observations of the Dobson and Brewer spectrometers and ozone radiosonde at Zhongshan and Syowa Antarctic research stations, for September 2004 to March 2009. Results show that mean bias error between Zhongshan (Syowa) and Ozone Monitor Instrument Total Ozone Mapping Spectrometer (OMI-TOMS) data are -0.06%±3.32% (-0.44%±2.41%); between it and OMI Multi Axis Differential Optical Absorption Spectroscopy (OMI-DOAS) data, the error is -0.34%±4.99% (-0.22%±4.85%). Mean absolute bias error values of OMI-TOMS data are less than those of OMI-DOAS. This means that total ozone of OMI-TOMS is closer to ground-based observation than that of OMI-DOAS. Comparison between direct observational total ozone of ground-based and integrated ozone from the ozone profile measured by ozone radiosonde shows that ozone amount calculated with the Solar Backscatter Ultraviolet (SBUV) method above balloon burst height is similar to corresponding Microwave Limb Sounder (MLS) data. Therefore, MLS data can be substituted with SBUV data to estimate ozone amount above that level. Mean bias error of the MLS ozone column is 2% compared with the ozonesonde column, with standard deviation within 9.5%. Comparison of different layers from ozone profiler and MLS data indicates that at the 215 hPa layer, the MLS ozone value is high, with relative deviation more than 20%. At the 100 hPa and 68 hPa layers, the MLS ozone value is also high. This deviation is mainly in spring, during Antarctic ozone hole appearance. In this period, at the height of severe ozone loss, relative deviation of MLS ozone values is especially large.

Cross-Calibration of the Total Ozone Unit (TOU) With the Ozone Monitoring Instrument (OMI) and SBUV/2 for Environmental Applications

A cross-sensor calibration technique is developed and applied to improve upon the prelaunch radiance calibration and characterization for the Total Ozone Unit (TOU) onboard the FengYun-3/A satellite. The Level 3 products from the National Aeronautics and Space Administration Ozone Monitoring Instrument (OMI) onboard the Earth Observing System Aura are used as input to a radiative transfer model to predict the TOU radiances and characterize the biases for the measurements over the Pacific Ocean in low- and midlatitudes. The coefficients are derived from a regression algorithm to adjust the TOU radiances. It is shown that, after the measurement bias correction, the biases between the retrieved total column ozone products from the TOU with those from the OMI Total Ozone Mapping Spectrometer (TOMS)-Version 8 products and those from a set of ground-based station measurements are 3 % and 5% , respectively. The variations in the estimated total ozone amounts from the TOU are consistent with those derived from Solar Backscatter Ultraviolet Radiometer instruments and OMI for a period from January 2010 to February 2011.

Overview of FY-3 Payload and Ground Application System

The payload on board the FengYun 3 (FY-3) satellite series has been providing critical observations to the Earth, and the observation data have been processed and distributed to various users by the corresponding ground application system. In this paper, the FY-3 payload and its future development plan are presented, and its ground system is introduced. The major characteristics of the FY-3 instruments and the requirement on the instruments for major applications are discussed as well. There are nine new instruments, including the Microwave Temperature Sounder (MWTS), Microwave Humidity Sounder (MWHS), Infrared Atmospheric Sounder (IRAS), Medium-Resolution Spectral Imager (MERSI), Microwave Radiation Imager (MWRI), Solar Backscatter Ultraviolet Sounder, Total Ozone Unit, Solar Irradiation Monitor, and Earth Radiation Measurement. The data quality from the IRAS, MWTS, MWHS, and MWRI has proved to be good, and according to our evaluation at the European Centre for Medium-Range Weather Forecasts (ECMWF), the data have a very high availability. The MERSI has 20 visible (VIS) and infrared (IR) channels, of which three are VIS channels with a 250-m spatial resolution, one is a near-IR channel with a 250-m spatial resolution, and one is a long-wave IR channel with a 250-m spatial resolution. The global data at a 250-m spatial resolution are very useful in weather, disaster, and environmental monitoring. Compared with the ground observations, the ozone products derived from the FY-3 series are highly accurate. We have completed the calibration and validation of these sensors and most products.

Calibration of the SBUV version 8.6 ozone data product

Abstract. This paper describes the calibration process for the Solar Backscatter Ultraviolet (SBUV) Version 8.6 (V8.6) ozone data product. Eight SBUV instruments have flown on NASA and NOAA satellites since 1970, and a continuous data record is available since November 1978. The accuracy of ozone trends determined from these data depends on the calibration and long-term characterization of each instrument. V8.6 calibration adjustments are determined at the radiance level, and do not rely on comparison of retrieved ozone products with other instruments. The primary SBUV instrument characterization is based on prelaunch laboratory tests and dedicated on-orbit calibration measurements. We supplement these results with "soft" calibration techniques using carefully chosen subsets of radiance data and information from the retrieval algorithm output to validate each instrument's calibration. The estimated long-term uncertainty in albedo is approximately ±0.8–1.2% (1σ) for most of the instruments. The overlap between these instruments and the Shuttle SBUV (SSBUV) data allows us to intercalibrate the SBUV instruments to produce a coherent V8.6 data set covering more than 32 yr. The estimated long-term uncertainty in albedo is less than 3% over this period.

Climatology 2011: An MLS and sonde derived ozone climatology for satellite retrieval algorithms

The ozone climatology used as the a priori for the version 8 Solar Backscatter Ultraviolet (SBUV) retrieval algorithms has been updated. The climatology was formed by combining data from Aura MLS (2004–2010) with data from balloon sondes (1988–2010). The Microwave Limb Sounder (MLS) instrument on Aura has excellent latitude coverage and measures ozone daily from the upper troposphere to the lower mesosphere. The new climatology consists of monthly average ozone profiles for ten degree latitude zones covering pressure altitudes from 0 to 65 km. Ozone below 8 km (below 12 km at high latitudes) is based on balloons sondes, while ozone above 16 km (21 km at high latitudes) is based on MLS measurements. Sonde and MLS data are blended in the transition region. Ozone accuracy in the upper troposphere is greatly improved because of the near uniform coverage by Aura MLS, while the addition of a large number of balloon sonde measurements improves the accuracy in the lower troposphere, in the tropics and southern hemisphere in particular. The addition of MLS data also improves the accuracy of the climatology in the upper stratosphere and lower mesosphere. The revised climatology has been used for the latest reprocessing of SBUV and TOMS satellite ozone data.

On the onset of polar mesospheric cloud seasons as observed by SBUV

This paper describes an investigation using data from the Solar Backscatter Ultraviolet (SBUV) satellite instruments to explore and understand variations in the timing of the onset of Polar Mesospheric Cloud (PMC) seasons. Previous work has shown that for several recent southern hemisphere (SH) seasons, the PMC season onset was controlled by the timing of the shift from winter to summer zonal wind flow in the SH stratosphere. We extend the analysis of PMC season onset to 28 years of SBUV observations, including both hemispheres. A multiple linear regression analysis of SBUV data from 1984 to 2011 suggests that the SH PMC season onset is delayed by one day for every day that the zonal wind at 65°S and 50 hPa (∼20 km) remains in a winter‐like state. In addition, we find that the solar cycle plays a role: The SH season onset is delayed by about ten days at solar maximum compared to solar minimum. In the NH, the PMC season onset is delayed by ∼7 days at solar maximum compared to solar minimum; variations in the NH stratospheric wind, however, are not correlated with the NH onset date. On the other hand, inter‐hemispheric teleconnections are important in the NH; a one‐day shift in the NH season onset corresponds to a shift of ∼1.4 m/s in the SH stratospheric wind at 60.0°S and 20 hPa (∼26 km). Neither the NH nor the SH season onset date is correlated with the Quasi‐Biennial Oscillation, North Atlantic Oscillation, Arctic Oscillation, or El Niño Southern Oscillation.

大气/真空环境紫外臭氧垂直探测仪光谱辐照度定标研究

大气/真空环境紫外臭氧垂直探测仪光谱辐照度定标研究

Solar response in tropical stratospheric ozone: a 3-D chemical transport model study using ERA reanalyses

Abstract. We have used an off-line 3-D chemical transport model (CTM) to investigate the 11-yr solar cycle response in tropical stratospheric ozone. The model is forced with European Centre for Medium-Range Weather Forecasts (ECMWF) (re)analysis (ERA-40/operational and ERA-Interim) data for the 1979–2005 time period. We have compared the modelled solar response in ozone to observation-based data sets that are constructed using satellite instruments such as Total Ozone Mapping Spectrometer (TOMS), Solar Backscatter UltraViolet instrument (SBUV), Stratospheric Aerosol and Gas Experiment (SAGE) and Halogen Occultation Experiment (HALOE). A significant difference is seen between simulated and observed ozone during the 1980s, which is probably due to inhomogeneities in the ERA-40 reanalyses. In general, the model with ERA-Interim dynamics shows better agreement with the observations from 1990 onwards than with ERA-40. Overall both standard model simulations are partially able to simulate a "double peak"-structured ozone solar response with a minimum around 30 km, and these are in better agreement with HALOE than SAGE-corrected SBUV (SBUV/SAGE) or SAGE-based data sets. In the tropical lower stratosphere (TLS), the modelled solar response with time-varying aerosols is amplified through aliasing with a volcanic signal, as the model overestimates ozone loss during high aerosol loading years. However, the modelled solar response with fixed dynamics and constant aerosols shows a positive signal which is in better agreement with SBUV/SAGE and SAGE-based data sets in the TLS. Our model simulations suggests that photochemistry contributes to the ozone solar response in this region. The largest model-observation differences occur in the upper stratosphere where SBUV/SAGE and SAGE-based data show a significant (up to 4%) solar response whereas the standard model and HALOE do not. This is partly due to a positive solar response in the ECMWF upper stratospheric temperatures which reduces the modelled ozone signal. The large positive upper stratospheric solar response seen in SBUV/SAGE and SAGE-based data can be reproduced in model runs with fixed dynamical fields (i.e. no inter-annual meteorological changes). As these runs effectively assume no long-term temperature changes (solar-induced or otherwise), it should provide an upper limit of the ozone solar response. Overall, full quantification of the solar response in stratospheric ozone is limited by differences in the observed data sets and by uncertainties in the solar response in stratospheric temperatures.

Interannual Changes of Stratospheric Temperature and Ozone: Forcing by Anomalous Wave Driving and the QBO

Abstract A 3D model of dynamics and photochemistry is used to investigate interannual changes of stratospheric dynamical and chemical structure through their dependence on tropospheric planetary waves and on the quasi-biennial oscillation (QBO). The integrations reproduce the salient features of the climate sensitivities of temperature and ozone, which have been composited from the observed records of ECMWF and the Total Ozone Mapping Spectrometer (TOMS). Characterized by a strong anomaly of one sign at polar latitudes and a comparatively weak anomaly of opposite sign at subpolar latitudes, each bears the signature of the residual mean circulation. The structure is very similar to that associated with the Arctic Oscillation. The integrations imply that, jointly, anomalous Eliassen–Palm (EP) flux transmitted from the troposphere by planetary waves and the QBO are the major mechanisms behind interannual changes in the stratosphere. An analogous conclusion follows from the observational record. During early winter, anomalous temperature and ozone are accounted for almost entirely by anomalous EP flux from the troposphere, as they are in the observational record. During late winter, both mechanisms are required to reproduce observed anomalies. Although the QBO forces anomalous structure equatorward of 40°N, the strong anomaly over the Arctic follows principally from anomalous upward EP flux. Reflecting anomalous wave driving of residual mean motion, the change of EP flux leads to anomalous downwelling of ozone-rich air. In concert with isentropic mixing by planetary waves, the anomalous enrichment that ensues at extratropical latitudes sharply modifies total ozone over the Arctic. Integrations distinguished by the omission of heterogeneous processes indicate that chemical destruction accounts for approximately 20% of the anomaly in Arctic ozone between warm and cold winters. Analogous to estimates derived from the observed record of the Solar Backscatter Ultraviolet, version 8 (SBUV-V8) instrument, the remaining approximately 80% follows from anomalous transport. The climate sensitivities of temperature and ozone describe random changes between years, introduced by anomalous EP flux and the QBO. Those interannual changes evolve with a particular seasonality. Like their structure, the seasonal dependence of anomalous temperature and ozone bears the signature of the residual mean circulation. Systematic changes in the observed record, which comprise stratospheric trends, have similar structure and seasonality.

Coherence of long-term stratospheric ozone vertical distribution time series used for the study of ozone recovery at a northern mid-latitude station

Abstract. The coherence of stratospheric ozone time series retrieved from various observational records is investigated at Haute-Provence Observatory (OHP–43.93° N, 5.71° E). The analysis is accomplished through the intercomparison of collocated ozone measurements of Light Detection and Ranging (lidar) with Solar Backscatter UltraViolet(/2) (SBUV(/2)), Stratospheric Aerosol and Gas Experiment II (SAGE~II), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS) and Aura and Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations as well as with in situ ozonesondes and ground-based Umkehr measurements performed at OHP. A detailed statistical study of the relative differences of ozone observations over the whole stratosphere is performed to detect any specific drift in the data. On average, all instruments show their best agreement with lidar at 20–40 km, where deviations are within ±5 %. Discrepancies are somewhat higher below 20 and above 40 km. The agreement with SAGE II data is remarkable since average differences are within ±1 % at 17–41 km. In contrast, Umkehr data underestimate systematically the lidar measurements in the whole stratosphere with a near zero bias at 16–8 hPa (~30 km). Drifts are estimated using simple linear regression for the data sets analysed in this study, from the monthly averaged difference time series. The derived values are less than ±0.5 % yr−1 in the 20–40 km altitude range and most drifts are not significant at the 2σ level. We also discuss the possibilities of extending the SAGE II and HALOE data with the GOMOS and Aura MLS data in consideration with relative offsets and drifts since the combination of such data sets are likely to be used for the study of stratospheric ozone recovery in the future.

A note on the comparison between total ozone from Oslo CTM2 and SBUV satellite data

The results of a comparison between total ozone amounts derived from solar backscatter ultraviolet (SBUV) satellite observations and those calculated from the chemical transport model Oslo CTM2 are presented for the period 2001–2007. Monthly mean total ozone amounts from improved model simulations were used to compute monthly, seasonal and annual zonal means over 10° latitude zones, and compared with respective satellite retrievals over the northern and southern hemispheres. The results show that the improved model simulations slightly underestimate total ozone over the northern hemisphere when compared with the satellites by 1.4% on average, and slightly overestimate total ozone over the southern extra-tropics, middle and high latitudes by 1.6% on average. The mean difference between the model- and satellite-derived total ozone columns from 75°S to 75°N is estimated to be about −0.3%. A linear regression analysis between the model- and satellite-derived total ozone data shows statistically significant correlations between the two data sets at all latitude zones (about +0.8 in the tropics and more than +0.9 over all other latitudes). The annual cycle of total ozone is shown to be well reproduced by the model at all latitudes.

Evaluation of AIM CIPS measurements of Polar Mesospheric Clouds by comparison with SBUV data

Polar Mesospheric Cloud (PMC) observations from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment are compared to results from the Solar Backscatter UltraViolet (SBUV/2) instrument for two PMC seasons in each hemisphere, from 2007–2009. For these comparisons, a CIPS cloud retrieval algorithm based on a technique similar to that used in the operational SBUV PMC retrievals was developed. CIPS nadir data analyzed this way agree with SBUV data to better than 1% (2%) for PMC occurrence frequency (albedo). Non-nadir, forward scattering CIPS data are also analyzed with the SBUV-type algorithm, enabling an indirect verification of the CIPS operational retrievals. CIPS operational PMC frequencies agree with these CIPS–SBUV-type retrievals to within 0.6% at 80–85° latitude, and are lower by 9.8% at 70–75° latitude. Overall, the comparisons show that the v3.20 CIPS operational cloud retrievals are valid for scientific research.

Quantifying stratospheric ozone trends: Complications due to stratospheric cooling

[1] Recent studies suggest that ozone turnaround (the second stage of ozone recovery) is near. Determining precisely when this occurs, however, will be complicated by greenhouse gas‐induced stratospheric cooling as ozone trends derived from profile data in different units and/or vertical co‐ordinates will not agree. Stratospheric cooling leads to simultaneous trends in air density and layer thicknesses, confounding the interpretation of ozone trends. A simple model suggests that instruments measuring ozone in different units may differ as to the onset of turnaround by a decade, with some indicting a continued decline while others an increase. This concept was illustrated by examining the long‐term (1979–2005) ozone trends in the SAGE (Stratospheric Aerosol and Gas Experiment) and SBUV (Solar Backscatter Ultraviolet) time series. Trends from SAGE, which measures number density as a function of altitude, and SBUV, which measures partial column as a function of pressure, are known to differ by 4–6%/decade in the upper stratosphere. It is shown that this long‐ standing difference can be reconciled to within 2%/decade when the trend in temperature is properly accounted for. Citation: McLinden, C. A., and V. Fioletov (2011), Quantifying stratospheric ozone trends: Complications due to stratospheric cooling, Geophys. Res. Lett., 38, L03808, doi:10.1029/2010GL046012.

Estimation of Arctic O3 loss during winter 2006/2007 using data assimilation and comparison with a chemical transport model

The evolution of Arctic stratospheric O3 throughout the winter and spring of 2006/2007 is estimated by a state-of-the-art chemical transport model (CTM) and by a 3D-Var assimilation system using O3 data from the Earth Observing System (EOS) Microwave Limb Sounder (MLS) and Solar Backscatter Ultraviolet Radiometer (SBUV/2) satellites. Modelled and assimilated O3 compare well with MLS measurements. The aim of this article is to compare O3 loss estimates derived from the CTM and data-assimilation results, and as a result point to further developments in the method of inferring O3 loss using data assimilation. The methods for inferring O3 loss are discussed and compared with other published methods. The assimilation-system vertical transport is found to be too fast, in agreement with an earlier study, although this affects only the O3 reference field used for the loss estimation. Improving the O3 reference in the assimilation method used here provides a maximum vortex average O3 loss range of 0.8–1.2 ppmv at 68 hPa and 1.0–1.5 ppmv at 46 hPa, peaking at the beginning of March. The corresponding CTM values are 1.4 and 1.6 ppmv, respectively, with the peak lagging the assimilation by a few days at 46 hPa. We show that using a passive tracer as reference for O3 loss does not provide the best estimate for polar stratospheric cloud (PSC)-related loss for this winter; up to 40% of total O3 loss is shown not to be related to PSCs or heterogenous chemistry. Hence, the use of a passive O3 reference for estimating PSC-related O3 loss should be made with care. In addition to the vortex average losses, we estimate an innermost vortex O3 loss of 1.4 ppmv due to PSCs only. Transport effects and differences between the CTM and the assimilation system are discussed, and possible improvements for both models are suggested. Copyright © Royal Meteorological Society and Crown Copyright, 2011

Seasonal persistence of ozone and zonal wind anomalies in the equatorial stratosphere

Analysis of the variability of equatorial ozone profiles in the Satellite Aerosol and Gas Experiment‐corrected Solar Backscatter Ultraviolet data set demonstrates a strong seasonal persistence of interannual ozone anomalies, revealing a seasonal dependence to equatorial ozone variability. In the lower stratosphere (40–25 hPa) and in the upper stratosphere (6–4 hPa), ozone anomalies persist from approximately November until June of the following year, while ozone anomalies in the layer between 16 and 10 hPa persist from June to December. Analysis of zonal wind fields in the lower stratosphere and temperature fields in the upper stratosphere reveals a similar seasonal persistence of the zonal wind and temperature anomalies associated with the quasi‐biennial oscillation (QBO). Thus, the persistence of interannual ozone anomalies in the lower and upper equatorial stratosphere, which are mainly associated with the well‐known QBO ozone signal through the QBO‐induced meridional circulation, is related to a newly identified seasonal persistence of the QBO itself. The upper stratospheric QBO ozone signal is argued to arise from a combination of QBO‐induced temperature and NOx perturbations, with the former dominating at 5 hPa and the latter at 10 hPa. Ozone anomalies in the transition zone between dynamical and photochemical control of ozone (16–10 hPa) are less influenced by the QBO signal and show a quite different seasonal persistence compared to the regions above and below.

SBUV observations of polar mesospheric clouds compared with MLS temperature and water vapor measurements

Earlier studies have shown that Polar Mesospheric Clouds (PMC) occur more frequently in the northern hemisphere (NH) than the SH, consistent with colder NH temperatures. Coincident PMC observations with the Solar Backscatter Ultraviolet instruments on the NOAA‐16 and NOAA‐18 satellite and temperature and water vapor measurements with the Microwave Limb Sounder on the Aura satellite support this result. These coincident measurements also show that, for similar temperatures and water vapor mixing ratios, PMCs occur more frequently and are brighter in the NH than the SH. Possible reasons for these hemispheric differences are discussed.

Are there urban signatures in the tropospheric ozone column products derived from satellite measurements?

Abstract. In view of the proposed geostationary satellite missions to monitor air quality from space, it is important to first assess the capability of the current suite of satellite instruments to provide information on the urban scale pollution. We explore the possibility of detecting urban signatures in the tropospheric column ozone data derived from Total Ozone Mapping Spectrometer (TOMS)/Solar Backscattered Ultraviolet (SBUV) and Ozone Monitoring Instrument (OMI)/Microwave Limb Sounder (MLS) satellite data. We find that distinct isolated plumes of tropospheric ozone near several large and polluted cities around the world may be detected in these data sets. The ozone plumes generally correspond with the tropospheric column NO2 plumes around these cities as observed by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument. Similar plumes are also seen in tropospheric mean ozone mixing ratio distribution after accounting for the surface and tropopause pressure variations. The total column ozone retrievals indicate fairly significant sensitivity to the lower troposphere over the polluted land areas, which might help explain these detections. These results indicate that ultraviolet (UV) measurements may, in principle, be able to capture the urban signatures and may have implications for future missions using geostationary satellites.