42 research outputs found
Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory
This work involves a first analysis of the systematic errors observed in the AOD retrieved at nighttime using the Sunâskyâlunar CE318-T photometer. In this respect, this paper is a first attempt to correct the AOD uncertainties that currently affect the lunar photometry by means of an empirical regression model. We have detected and corrected an important bias correlated to the Moon's phase and zenith angles, especially at longer wavelength channels.AERONET Sun photometers at Izaña have been calibrated
within the AERONET Europe TNA, supported by the European
Unionâs Horizon 2020 research and innovation program under
grant agreement no. 654109 (ACTRIS-2)
Aerosol optical properties and direct radiative forcing based on measurements from the China Aerosol Remote Sensing Network (CARSNET) in eastern China
Aerosol pollution in eastern China is an unfortunate consequence of the region's rapid economic and industrial growth. Here, sun photometer measurements from seven sites in the Yangtze River Delta (YRD) from 2011 to 2015 were used to characterize the climatology of aerosol microphysical and optical properties, calculate direct aerosol radiative forcing (DARF) and classify the aerosols based on size and absorption. Bimodal size distributions were found throughout the year, but larger volumes and effective radii of fine-mode particles occurred in June and September due to hygroscopic growth and/or cloud processing. Increases in the fine-mode particles in June and September caused AOD440ânmâ>â1.00 at most sites, and annual mean AOD440ânm values of 0.71-0.76 were found at the urban sites and 0.68 at the rural site. Unlike northern China, the AOD440ânm was lower in July and August (âŒâ0.40-0.60) than in January and February (0.71-0.89) due to particle dispersion associated with subtropical anticyclones in summer. Low volumes and large bandwidths of both fine-mode and coarse-mode aerosol size distributions occurred in July and August because of biomass burning. Single-scattering albedos at 440ânm (SSA440ânm) from 0.91 to 0.94 indicated particles with relatively strong to moderate absorption. Strongly absorbing particles from biomass burning with a significant SSA wavelength dependence were found in July and August at most sites, while coarse particles in March to May were mineral dust. Absorbing aerosols were distributed more or less homogeneously throughout the region with absorption aerosol optical depths at 440ânm âŒâ0.04-0.06, but inter-site differences in the absorption Angström exponent indicate a degree of spatial heterogeneity in particle composition. The annual mean DARF was â93â±â44 to â79â±â39âWâmâ2 at the Earth's surface and âŒââ40âWâmâ2 at the top of the atmosphere (for the solar zenith angle range of 50 to 80â) under cloud-free conditions. The fine mode composed a major contribution of the absorbing particles in the classification scheme based on SSA, fine-mode fraction and extinction Angström exponent. This study contributes to our understanding of aerosols and regional climate/air quality, and the results will be useful for validating satellite retrievals and for improving climate models and remote sensing algorithms
Evaluation of night-time aerosols measurements and lunar irradiance models in the frame of the first multi-instrument nocturnal intercomparison campaign
The first multi-instrument nocturnal aerosol optical depth (AOD) intercomparison campaign was held at the high-mountain Izaña Observatory (Tenerife, Spain) in June 2017, involving 2-min synchronous measurements from two different types of lunar photometers (Cimel CE318-T and Moon Precision Filter Radiometer, LunarPFR) and one stellar photometer. The Robotic Lunar Observatory (ROLO) model developed by the U.S. Geological Survey (USGS) was compared with the open-access ROLO Implementation for Moon photometry Observation (RIMO) model. Results showed rather small differences at Izaña over a 2-month time period covering June and July, 2017 (±0.01 in terms of AOD calculated by means of a day/night/day coherence test analysis and ± 2% in terms of lunar irradiance). The RIMO model has been used in this field campaign to retrieve AOD from lunar
photometric measurements. No evidence of significant differences with the Moon's phase angle was found when comparing raw signals of the six Cimel photometers involved in this field campaign. The raw signal comparison of the participating lunar photometers (Cimel and LunarPFR) performed at coincident wavelengths showed consistent measurements and AOD differences within their combined uncertainties at 870 nm and 675 nm. Slightly larger AOD deviations were observed at 500 nm, pointing to some unexpected instrumental variations during the measurement period. Lunar irradiances retrieved using RIMO for phase angles varying between 0° and 75° (full Moon to near quarter Moon) were compared to the irradiance variations retrieved by Cimel and LunarPFR photometers. Our results showed a relative agreement within ± 3.5% between the RIMO model and the photometer-based lunar irradiances. The AOD retrieved by performing a Langley-plot calibration each night showed a remarkable agreement (better than 0.01) between the lunar photometers. However, when applying the Lunar-Langley calibration using RIMO, AOD differences of up to 0.015 (0.040 for 500 nm) were found, with differences increasing with the Moon's phase angle. These differences are thought to be partly due to the uncertainties in the irradiance models, as well as instrumental deficiencies yet to be fully understood. High AOD variability in stellar measurements was detected during the campaign. Nevertheless, the observed AOD differences in the Cimel/stellar comparison were within the expected combined uncertainties of these two photometric techniques. Our results indicate that lunar photometry is a more reliable technique, especially for low aerosol loading conditions. The uncertainty analysis performed in this paper shows that the combined standard AOD uncertainty in lunar photometry is dependent on the calibration technique (up to 0.014 for Langley-plot with illumination-based correction, 0.012â0.022 for Lunar-Langley calibration, and up to 0.1 for the Sun-Moon Gain Factor method). This analysis also corroborates that the uncertainty of the lunar irradiance model used for AOD calculation is
within the 5â10% expected range. This campaign has allowed us to quantify the important technical difficulties that still exist when routinely monitoring aerosol optical properties at night-time. The small AOD differences observed between the three types of photometers involved in the campaign are only detectable under pristine sky conditions such as those found in this field campaign. Longer campaigns are necessary to understand the observed discrepancies between instruments as well as to provide more conclusive results about the uncertainty involved in the lunar irradiance models.This work has been developed within the framework of the activities of the World Meteorological Organization (WMO) Commission for
Instruments and Methods of Observations (CIMO) Izaña Testbed for Aerosols and Water Vapour Remote Sensing Instruments. AERONET sun
photometers at Izaña have been calibrated within the AERONET Europe TNA, supported by the European Unionâs Horizon 2020 research and
innovation program under grant agreement no. 654109 (ACTRISâ2). CE318-T linearity check has been performed as part of the ESA-funded project âLunar spectral irradiance measurement and modelling for absolute calibration of EO optical sensorsâ under ESA contract number:
4000121576/17/NL/AF/hh. LunarPFR has been performing measurements since 2014 in Norway thanks to Svalbard Science Forum funded project, 2014â2016. The authors would like to thank AERONET team for their support and also to NASAâs Navigation and Ancillary Information Facility (NAIF) at the Jet Propulsion Laboratory to help the implementation of the âSPICEâ ancillary information system used in this study. We also thank Izaña's ITs for their work to implement the RIMO model in the free-access server. Special thanks should be given to Tom Stone, who has kindly provided us with the USGS/ROLO irradiance values used in the model comparison analysis. This work has also received funding from the European Unionâs Horizon 2020 research and innovation programme and from Marie SkĆodowska-Curie Individual Fellowships (IF) ACE-GFAT (grant agreement no. 659398). The authors are grateful to Spanish MINECO (CTM2015-66742-R) and Junta de Castilla y LeĂłn (VA100P17)
Evaluation of night-time aerosols measurements and lunar irradiance models in the frame of the first multi-instrument nocturnal intercomparison campaign
The first multi-instrument nocturnal aerosol optical depth (AOD) intercom-parison campaign was held at the high-mountain Iza Ìna Observatory (Tener-ife, Spain) in June 2017, involving 2-minutes synchronous measurements fromtwo different types of lunar photometers (Cimel CE318-T and Moon Preci-sion Filter Radiometer, LunarPFR) and one stellar photometer. The Robotic Lunar Observatory (ROLO) model developed by the U.S. Geological Survey(USGS) was compared with the open-access ROLO Implementation for Moonphotometry Observation (RIMO) model. Results showed rather small differ-ences at Iza Ìna over a 2-month time period covering June and July, 2017(±0.01 in terms of AOD calculated by means of a day/night/day coherencetest analysis and±2 % in terms of lunar irradiance). The RIMO model hasbeen used in this field campaign to retrieve AOD from lunar photometricmeasurements. No evidence of significant differences with the Moonâs phase angle wasfound when comparing raw signals of the six Cimel photometers involved inthis field campaign.The raw signal comparison of the participating lunar photometers (Cimeland LunarPFR) performed at coincident wavelengths showed consistent mea-surements and AOD differences within their combined uncertainties at 870 nmand 675 nm. Slightly larger AOD deviations were observed at 500 nm, point-ing to some unexpected instrumental variations during the measurement pe-riod.Lunar irradiances retrieved using RIMO for phase angles varying between0âŠand 75âŠ(full Moon to near quarter Moon) were compared to the irradi-ance variations retrieved by Cimel and LunarPFR photometers. Our resultsshowed a relative agreement within±3.5 % between the RIMO model andthe photometer-based lunar irradiances.The AOD retrieved by performing a Langley-plot calibration each nightshowed a remarkable agreement (better than 0.01) between the lunar pho-tometers. However, when applying the Lunar-Langley calibration using RIMO,AOD differences of up to 0.015 (0.040 for 500 nm) were found, with differ-ences increasing with the Moonâs phase angle. These differences are thoughtto be partly due to the uncertainties in the irradiance models, as well asinstrumental deficiencies yet to be fully understood.High AOD variability in stellar measurements was detected during thecampaign. Nevertheless, the observed AOD differences in the Cimel/stellarcomparison were within the expected combined uncertainties of these twophotometric techniques. Our results indicate that lunar photometry is amore reliable technique, especially for low aerosol loading conditions.The uncertainty analysis performed in this paper shows that the com-bined standard AOD uncertainty in lunar photometry is dependent on thecalibration technique (up to 0.014 for Langley-plot with illumination-basedcorrection, 0.012-0.022 for Lunar-Langley calibration, and up to 0.1 for the 2 Sun-Moon Gain Factor method). This analysis also corroborates that theuncertainty of the lunar irradiance model used for AOD calculation is withinthe 5-10 % expected range.This campaign has allowed us to quantify the important technical diffi-culties that still exist when routinely monitoring aerosol optical propertiesat night-time. The small AOD differences observed between the three typesof photometers involved in the campaign are only detectable under pristinesky conditions such as those found in this field campaign. Longer campaignsare necessary to understand the observed discrepancies between instrumentsas well as to provide more conclusive results about the uncertainty involvedin the lunar irradiance model
Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory
This work is a first approach to correct the systematic errors
observed in the aerosol optical depth (AOD) retrieved at nighttime using
lunar photometry and calibration techniques dependent on the lunar irradiance
model. To this end, nocturnal AOD measurements were performed in 2014 using
the CE318-T master Sunâskyâlunar photometer (lunar Langley calibrated) at
the Izaña high mountain observatory. This information has been restricted to 59
nights characterized as clean and stable according to lidar vertical
profiles. A phase angle dependence as well as an asymmetry within the Moon's
cycle of the Robotic Lunar Observatory (ROLO) model could be deduced from the comparison in this
59-night period of the CE318-T calibration performed by means of the
lunar Langley calibration
and the calibration performed every single night by means of
the common Langley technique. Nocturnal AOD has also been compared in the
same period with a reference AOD based on daylight AOD extracted from the
AErosol RObotic NETwork (AERONET) at the same station. Considering stable conditions, the
difference ÎAODfit, between AOD from lunar observations
and the linearly interpolated AOD (the reference) from daylight data, has
been calculated. The results show that ÎAODfit values are
strongly affected by the Moon phase and zenith angles. This dependency has been
parameterized using an empirical model with two independent variables (Moon
phase and zenith angles) in order to correct the AOD for these residual
dependencies. The correction of this parameterized dependency has been
checked at four stations with quite different environmental conditions
(Izaña, Lille, Carpentras and Dakar) showing a significant reduction of the
AOD dependence on phase and zenith angles and an improved agreement with
daylight reference data. After the correction, absolute AOD differences for
dayânightâday clean and stable transitions remain below 0.01 for all
wavelengths
Overview of the Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate (ChArMEx/ADRIMED) summer 2013 campaign
The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-climate interactions. A special observing period (SOP-1a) including intensive airborne measurements was performed in the framework of the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) project during the Mediterranean dry season over the western and central Mediterranean basins, with a focus on aerosol-radiation measurements and their modeling. The SOP-1a took place from 11 June to 5 July 2013. Airborne measurements were made by both the ATR-42 and F-20 French research aircraft operated from Sardinia (Italy) and instrumented for in situ and remote-sensing measurements, respectively, and by sounding and drifting balloons, launched in Minorca. The experimental setup also involved several ground-based measurement sites on islands including two ground-based reference stations in Corsica and Lampedusa and secondary monitoring sites in Minorca and Sicily. Additional measurements including lidar profiling were also performed on alert during aircraft operations at EARLINET/ACTRIS stations at Granada and Barcelona in Spain, and in southern Italy. Remote-sensing aerosol products from satellites (MSG/SEVIRI, MODIS) and from the AERONET/PHOTONS network were also used. Dedicated meso-scale and regional modeling experiments were performed in relation to this observational effort. We provide here an overview of the different surface and aircraft observations deployed during the ChArMEx/ADRIMED period and of associated modeling studies together with an analysis of the synoptic conditions that determined the aerosol emission and transport. Meteorological conditions observed during this campaign (moderate temperatures and southern flows) were not favorable to producing high levels of atmospheric pollutants or intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign, with the main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 and 0.6 (at 440 nm) over the western and central Mediterranean basins. One important point of this experiment concerns the direct observations of aerosol extinction onboard the ATR-42, using the CAPS system, showing local maxima reaching up to 150Mm(-1) within the dust plume. Non-negligible aerosol extinction (about 50Mm(-1)) has also been observed within the marine boundary layer (MBL). By combining the ATR- 42 extinction coefficient observations with absorption and scattering measurements, we performed a complete optical closure revealing excellent agreement with estimated optical properties. This additional information on extinction properties has allowed calculation of the dust single scattering albedo (SSA) with a high level of confidence over the western Mediterranean. Our results show a moderate variability from 0.90 to 1.00 (at 530 nm) for all flights studied compared to that reported in the literature on this optical parameter. Our results underline also a relatively low difference in SSA with values derived near dust sources. In parallel, active remote-sensing observations from the surface and onboard the F-20 aircraft suggest a complex vertical structure of particles and distinct aerosol layers with sea spray and pollution located within the MBL, and mineral dust and/or aged North American smoke particles located above (up to 6â7 km in altitude). Aircraft and balloon-borne observations allow one to investigate the vertical structure of the aerosol size distribution showing particles characterized by a large size (> 10 ÎŒm in diameter) within dust plumes. In most of cases, a coarse mode characterized by an effective diameter ranging between 5 and 10 ÎŒm, has been detected above the MBL. In terms of shortwave (SW) direct forcing, in situ surface and aircraft observations have been merged and used as inputs in 1-D radiative transfer codes for calculating the aerosol direct radiative forcing (DRF). Results show significant surface SW instantaneous forcing (up to (-90)Wm(-2) at noon). Aircraft observations provide also original estimates of the vertical structure of SW and LW radiative heating revealing significant instantaneous values of about 5 K per day in the solar spectrum (for a solar angle of 30 ) within the dust layer. Associated 3-D modeling studies from regional climate (RCM) and chemistry transport (CTM) models indicate a relatively good agreement for simulated AOD compared with observations from the AERONET/PHOTONS network and satellite data, especially for long-range dust transport. Calculations of the 3-D SW (clear-sky) surface DRF indicate an average of about -10 to -20Wm(-2) (for the whole period) over the Mediterranean Sea together with maxima (-50Wm(-2)) over northern Africa. The top of the atmosphere (TOA) DRF is shown to be highly variable within the domain, due to moderate absorbing properties of dust and changes in the surface albedo. Indeed, 3-D simulations indicate negative forcing over the Mediterranean Sea and Europe and positive forcing over northern Africa. Finally, a multiyear simulation, performed for the 2003 to 2009 period and including an oceanâatmosphere (OâA) coupling, underlines the impact of the aerosol direct radiative forcing on the sea surface temperature, OâA fluxes and the hydrological cycle over the Mediterranean.French National Research Agency (ANR)
ANR-11-BS56-0006ADEMEFrench Atomic Energy CommissionCNRS-INSU and Meteo-France through the multidisciplinary programme MISTRALS (Mediterranean Integrated Studies aT Regional And Local Scales)CORSiCA project - Collectivite Territoriale de Corse through Fonds Europeen de Developpement Regional of the European Operational ProgramContrat de Plan Etat-RegionEuropean Union's Horizon 2020 research and innovation program
654169Spanish Ministry of Economy and Competitivity
TEC2012-34575Science and Innovation
UNPC10-4E-442European Union (EU)Department of Economy and Knowledge of the Catalan Autonomous Government
SGR 583Andalusian Regional Government
P12-RNM-2409Spanish Government
CGL2013-45410-R
26225
Assessment of Sun photometer Langley calibration at the high-elevation sites Mauna Loa and Izaña
The aim of this paper is to analyze the suitability of the high-mountain
stations Mauna Loa and Izaña for Langley plot calibration of Sun
photometers. Thus the aerosol optical depth (AOD) characteristics and
seasonality, as well as the cloudiness, have been investigated in order to
provide a robust estimation of the calibration uncertainty as well as the
number of days that are suitable for Langley calibrations. The data used for
the investigations belong to the AERONET and GAW-PFR networks, which maintain
reference Sun photometers at these stations with long measurement records:
22 years at Mauna Loa and 15 years at Izaña. In terms of clear-sky and
stable aerosol conditions, Mauna Loa (3397 m a.s.l.) exhibits on average
377 Langley plots (243 morning and 134 afternoon)
per year suitable for Langley plot calibration, whereas Izaña
(2373 m a.s.l.) shows 343 Langley plots (187 morning and 155 afternoon) per
year. The background AOD (500 nm) values, on days that are favorable for
Langley calibrations, are in the range 0.01â0.02 throughout the year, with
well-defined seasonality that exhibits a spring maximum at both stations plus
a slight summer increase at Izaña. The statistical analysis of the
long-term determination of extraterrestrial signals yields to a calibration
uncertainty of ââŒâ 0.25â0.5 %, this uncertainty being smaller in the
visible and near-infrared wavelengths and larger in the ultraviolet
wavelengths. This is due to atmospheric variability produced by changes in
several factors, mainly the AOD. The uncertainty cannot be reduced based only
on quality criteria of individual Langley plots and averaging over several
days is shown to reduce the uncertainty to the needed levels for reference
Sun photometers.</p
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Radar altimetry measurements over antarctic ice sheet: A focus on antenna polarization and change in backscatter problems
ISI Document Delivery No.: 010LG Times Cited: 1 Cited Reference Count: 25 Cited References: Arthern RJ, 2001, J GEOPHYS RES-ATMOS, V106, P33471, DOI 10.1029/2001JD000498 Brenner AC, 2007, IEEE T GEOSCI REMOTE, V45, P321, DOI [10.1109/TGRS.2006.887172, 10.1106/TGRS.2006.887172] Davis CH, 2004, IEEE T GEOSCI REMOTE, V42, P2437, DOI 10.1109/TGRS.2004.836789 DAVIS CH, 1993, J GLACIOL, V39, P687 FUNG AK, 1982, IEEE T GEOSCI REMOTE, V20, P528, DOI 10.1109/TGRS.1982.350421 Lacroix P, 2009, REMOTE SENS ENVIRON, V113, P2633, DOI 10.1016/j.rse.2009.07.019 Lacroix P, 2008, REMOTE SENS ENVIRON, V112, P1712, DOI 10.1016/j.rse.2007.08.022 Legresy B, 1999, GEOPHYS RES LETT, V26, P2231, DOI 10.1029/1999GL900531 Legresy B, 1998, J GLACIOL, V44, P197 Legresy B, 2005, REMOTE SENS ENVIRON, V95, P150, DOI 10.1016/j.rse.2004.11.018 Li J., 2002, INT S PHYS MECH PROC, P233 Li J, 2004, ANN GLACIOL, V38, P309, DOI 10.3189/172756404781814988 Matzler C., 1987, Remote Sensing Reviews, V2 Pritchard HD, 2009, NATURE, V461, P971, DOI 10.1038/nature08471 Remy F, 2009, REMOTE SENS-BASEL, V1, P1212, DOI 10.3390/rs1041212 Remy F, 2006, IEEE T GEOSCI REMOTE, V44, P3289, DOI 10.1109/TGRS.2006.878444 RIDLEY JK, 1988, INT J REMOTE SENS, V9, P601 Tran N, 2008, IEEE T GEOSCI REMOTE, V46, P3694, DOI 10.1109/TGRS.2008.2000818 Vincent P, 2006, SENSORS-BASEL, V6, P208, DOI 10.3390/s6030208 Wingham D., 2009, GEOPHYS RES LETT, V36 Wingham DJ, 2006, PHILOS T R SOC A, V364, P1627, DOI 10.1098/rsta.2006.1792 Wingham DJ, 2006, ADV SPACE RES-SERIES, V37, P841, DOI 10.1016/j.asr.2005.07.027 Wingham DJ, 1998, SCIENCE, V282, P456, DOI 10.1126/science.282.5388.456 Zwally HJ, 2005, J GLACIOL, V51, P509, DOI 10.3189/172756505781829007 Zwally HJ, 2002, J GLACIOL, V48, P199, DOI 10.3189/172756502781831403 Remy, F. Flament, T. Blarel, F. Benveniste, J. 1 ELSEVIER SCI LTD OXFORD ADV SPACE RESIn this paper, we investigate the impact of the error due to the penetration of the altimetric wave within the snowpack. The phenomenon has two different impacts. The first one, due to temporal change in snow characteristics, affects the ice sheet volume trend as derived from altimetric series. The second one, because of both the anisotropy of the ice sheet surface properties and of the linear antenna polarization, introduces a difference in measurements at crossover points. These two phenomena are the cause of what are probably the most critical limitations to the interpretation of long-term altimetric series in term of mass balance and to the comparison between or data fusion of different missions. Moreover, they will lead to the largest error when comparing data from EnviSat with data from CryoSat, because of the different orbits, or with data from AltiKa, because of the different radar frequencies. We show that waveform distortions due to snow characteristics fluctuation are complex. In the central part of the East Antarctica, the height and the leading edge width fluctuations vary together while elsewhere, height fluctuations may occur with no variations in the waveform shape, mostly during winter. As a consequence, these induced errors cannot be corrected with solely the help of the backscatter: waveform shape parameters are also needed. They are however not enough to fully correct these two errors. We propose an empirical correction for these effects. We show that crossover differences may be significantly reduced to up 22 cm. In terms of volume change, the estimation may vary up to 4 cm/yr at cross-overs depending on the correction used and is reduced in average to 2.3 cm/yr with our correction. The difference between the height trends estimated with both corrections is weak in average but may locally reach 5 cm/yr with a clear geographical pattern. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved