scholarly journals Averaging bias correction for the future space-borne methane IPDA lidar mission MERLIN

2018 ◽  
Vol 11 (10) ◽  
pp. 5865-5884 ◽  
Author(s):  
Yoann Tellier ◽  
Clémence Pierangelo ◽  
Martin Wirth ◽  
Fabien Gibert ◽  
Fabien Marnas
Keyword(s):  
Systematic Error ◽  
Optical Depth ◽  
Random Noise ◽  
Reference Value ◽  
Surface Flux ◽  
Differential Absorption ◽  
Satellite Mission ◽  
Space Agency ◽  
Future Space ◽  
Air Mixing

Abstract. The CNES (French Space Agency) and DLR (German Space Agency) project MERLIN is a future integrated path differential absorption (IPDA) lidar satellite mission that aims at measuring methane dry-air mixing ratio columns (XCH4) in order to improve surface flux estimates of this key greenhouse gas. To reach a 1 % relative random error on XCH4 measurements, MERLIN signal processing performs an averaging of data over 50 km along the satellite trajectory. This article discusses how to process this horizontal averaging in order to avoid the bias caused by the non-linearity of the measurement equation and measurements affected by random noise and horizontal geophysical variability. Three averaging schemes are presented: averaging of columns of XCH4, averaging of columns of differential absorption optical depth (DAOD) and averaging of signals. The three schemes are affected both by statistical and geophysical biases that are discussed and compared, and correction algorithms are developed for the three schemes. These algorithms are tested and their biases are compared on modelled scenes from real satellite data. To achieve the accuracy requirements that are limited to 0.2 % relative systematic error (for a reference value of 1780 ppb), we recommend performing the averaging of signals corrected from the statistical bias due to the measurement noise and from the geophysical bias mainly due to variations of methane optical depth and surface reflectivity along the averaging track. The proposed method is compliant with the mission relative systematic error requirements dedicated to averaging algorithms of 0.06 % (±1 ppb for XCH4=1780ppb) for all tested scenes and all tested ground reflectivity values.

scholarly journals Averaging Bias Correction for the Future Space-borne Methane IPDA Lidar Mission MERLIN

2018 ◽  
Author(s):  
Yoann Tellier ◽  
Clémence Pierangelo ◽  
Martin Wirth ◽  
Fabien Gibert ◽  
Fabien Marnas
Keyword(s):  
Systematic Error ◽  
Optical Depth ◽  
Random Noise ◽  
Reference Value ◽  
Surface Flux ◽  
Satellite Mission ◽  
Future Space ◽  
Air Mixing ◽  
Surface Reflectivity ◽  
Satellite Trajectory

Abstract. The CNES/DLR project MERLIN is a future IPDA lidar satellite mission that aims at measuring methane dry-air mixing ratio columns (XCH4) in order to improve surface flux estimates of this key greenhouse gas. To reach a 1 % relative random error on XCH4 measurements, MERLIN signal processing performs an averaging of data over 50 km along the satellite trajectory. This article discusses how to process this horizontal averaging in order to avoid the bias caused by the non-linearity of the measurement equation with measurements affected by random noise and horizontal geophysical variability. Three averaging schemes are presented: averaging of columns of XCH4, averaging of columns of Differential Absorption Optical Depth (DAOD) and averaging of signals. The three schemes are affected both by statistical and geophysical biases that are discussed and compared and correction algorithms are developed for the three schemes. These algorithms are tested and their biases are compared on modeled scenes from real satellite data. To achieve the accuracy requirements that are limited to 0.2 % relative systematic error (for a reference value of 1780 ppb), we recommend performing the averaging of signals corrected from the statistical bias due to the measurement noise and from the geophysical bias mainly due to variations of methane optical depth and surface reflectivity along the averaging track. The proposed method is compliant with the mission relative systematic error requirements dedicated to averaging algorithms of 0.07 % (± 1 ppb for XCH4 = 1780 ppb) for all tested scenes and all tested ground reflectivity values.

scholarly journals Averaging Bias Correction for Future IPDA Lidar Mission MERLIN

2018 ◽  
Vol 176 ◽  
pp. 02020
Author(s):  
Yoann Tellier ◽  
Clémence Pierangelo ◽  
Martin Wirth ◽  
Fabien Gibert
Keyword(s):  
Signal Processing ◽  
Bias Correction ◽  
Surface Flux ◽  
Mixing Ratio ◽  
Satellite Mission ◽  
Dry Air ◽  
Non Linear ◽  
Air Mixing ◽  
Lidar Equation

The CNES/DLR MERLIN satellite mission aims at measuring methane dry-air mixing ratio column (XCH4) and thus improving surface flux estimates. In order to get a 1% precision on XCH4 measurements, MERLIN signal processing assumes an averaging of data over 50 km. The induced biases due to the non-linear IPDA lidar equation are not compliant with accuracy requirements. This paper analyzes averaging biases issues and suggests correction algorithms tested on realistic simulated scenes.

scholarly journals Airborne demonstration of atmospheric oxygen optical depth measurements with an integrated path differential absorption lidar

2017 ◽  
Vol 25 (23) ◽  
pp. 29307 ◽  
Author(s):  
Haris Riris ◽  
Michael Rodriguez ◽  
Jianping Mao ◽  
Graham Allan ◽  
James Abshire
Keyword(s):  
Optical Depth ◽  
Atmospheric Oxygen ◽  
Differential Absorption ◽  
Differential Absorption Lidar

scholarly journals Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

2020 ◽  
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Atmospheric Aerosols ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus candidate mission for anthropogenic CO2 monitoring (CO2M). To this end, we compare aerosol-induced XCO2 errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm, and a spread (defined as half of the 15.9th to the 84.1th percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to a worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise using both MAP and spectrometer measurements of the synthetic scenes delivers XCO2 errors with an overall bias of −0.004 ppm and a spread of 0.54 ppm, implying compliance with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.

Galileo Case Study

2013 ◽  
pp. 251-282
Author(s):  
Aggelos Liapis ◽  
Evangelos Argyzoudis
Keyword(s):  
Data Exchange ◽  
Collaborative Work ◽  
Effective Interaction ◽  
European Space Agency ◽  
Space Missions ◽  
Working Environment ◽  
Task Forces ◽  
Space Agency ◽  
Future Space ◽  
Collaborative Working

The Concurrent Design Facility (CDF) of the European Space Agency (ESA) allows a team of experts from several disciplines to apply concurrent engineering for the design of future space missions. It facilitates faster and effective interaction of all disciplines involved, ensuring consistent and high-quality results. It is primarily used to assess the technical and financial feasibility of future space missions and new spacecraft concepts, though for some projects, the facilities and the data exchange model are used during later phases. This chapter focuses on the field of computer supported collaborative work (CSCW) and its supporting areas whose mission is to support interaction between people, using computers as the enabling technology. Its aim is to present the design and implementation framework of a semantically driven, collaborative working environment (CWE) that allows ESA’s CDF to be used by projects more extensively and effectively during project meetings, task forces, and reviews.

scholarly journals OLCI A/B Tandem Phase Analysis, Part 1: Level 1 Homogenisation and Harmonisation

2020 ◽  
Vol 12 (11) ◽  
pp. 1804 ◽  
Author(s):  
Nicolas Lamquin ◽  
Sébastien Clerc ◽  
Ludovic Bourg ◽  
Craig Donlon
Keyword(s):  
European Space Agency ◽  
Companion Paper ◽  
The Other ◽  
Satellite Mission ◽  
Space Agency ◽  
The Future ◽  
Level 1 ◽  
Level 2 ◽  
Very High ◽  
Sentinel 2

Copernicus is a European system for monitoring the Earth in support of European policy. It includes the Sentinel-3 satellite mission which provides reliable and up-to-date measurements of the ocean, atmosphere, cryosphere, and land. To fulfil mission requirements, two Sentinel-3 satellites are required on-orbit at the same time to meet revisit and coverage requirements in support of Copernicus Services. The inter-unit consistency is critical for the mission as more S3 platforms are planned in the future. A few weeks after its launch in April 2018, the Sentinel-3B satellite was manoeuvred into a tandem configuration with its operational twin Sentinel-3A already in orbit. Both satellites were flown only thirty seconds apart on the same orbit ground track to optimise cross-comparisons. This tandem phase lasted from early June to mid October 2018 and was followed by a short drift phase during which the Sentinel-3B satellite was progressively moved to a specific orbit phasing of 140° separation from the sentinel-3A satellite. In this paper, an output of the European Space Agency (ESA) Sentinel-3 Tandem for Climate study (S3TC), we provide a full methodology for the homogenisation and harmonisation of the two Ocean and Land Colour Instruments (OLCI) based on the tandem phase. Homogenisation adjusts for unavoidable slight spatial and spectral differences between the two sensors and provide a basis for the comparison of the radiometry. Persistent radiometric biases of 1–2% across the OLCI spectrum are found with very high confidence. Harmonisation then consists of adjusting one instrument on the other based on these findings. Validation of the approach shows that such harmonisation then procures an excellent radiometric alignment. Performed on L1 calibrated radiances, the benefits of harmonisation are fully appreciated on Level 2 products as reported in a companion paper. Whereas our methodology aligns one sensor to behave radiometrically as the other, discussions consider the choice of the reference to be used within the operational framework. Further exploitation of the measurements indeed provides evidence of the need to perform flat-fielding on both payloads, prior to any harmonisation. Such flat-fielding notably removes inter-camera differences in the harmonisation coefficients. We conclude on the extreme usefulness of performing a tandem phase for the OLCI mission continuity as well as for any optical mission to which the methodology presented in this paper applies (e.g., Sentinel-2). To maintain the climate record, it is highly recommended that the future Sentinel-3C and Sentinel-3D satellites perform tandem flights when injected into the Sentinel-3 time series.

scholarly journals The impact of neglecting ice phase on cloud optical depth retrievals from AERONET cloud mode observations

2019 ◽  
Vol 12 (9) ◽  
pp. 5087-5099 ◽  
Author(s):  
Jonathan K. P. Shonk ◽  
Jui-Yuan Christine Chiu ◽  
Alexander Marshak ◽  
David M. Giles ◽  
Chiung-Huei Huang ◽  
...  
Keyword(s):  
Linear Equation ◽  
Optical Depth ◽  
Climate Models ◽  
Deep Convection ◽  
Surface Flux ◽  
Climate Modelling ◽  
Cloud Optical Depth ◽  
The Impact ◽  
Ice Fraction

Abstract. Clouds present many challenges to climate modelling. To develop and verify the parameterisations needed to allow climate models to represent cloud structure and processes, there is a need for high-quality observations of cloud optical depth from locations around the world. Retrievals of cloud optical depth are obtainable from radiances measured by Aerosol Robotic Network (AERONET) radiometers in “cloud mode” using a two-wavelength retrieval method. However, the method is unable to detect cloud phase, and hence assumes that all of the cloud in a profile is liquid. This assumption has the potential to introduce errors into long-term statistics of retrieved optical depth for clouds that also contain ice. Using a set of idealised cloud profiles we find that, for optical depths above 20, the fractional error in retrieved optical depth is a linear function of the fraction of the optical depth that is due to the presence of ice cloud (“ice fraction”). Clouds that are entirely ice have positive errors with magnitudes of the order of 55 % to 70 %. We derive a simple linear equation that can be used as a correction at AERONET sites where ice fraction can be independently estimated. Using this linear equation, we estimate the magnitude of the error for a set of cloud profiles from five sites of the Atmospheric Radiation Measurement programme. The dataset contains separate retrievals of ice and liquid retrievals; hence ice fraction can be estimated. The magnitude of the error at each location was related to the relative frequencies of occurrence in thick frontal cloud at the mid-latitude sites and of deep convection at the tropical sites – that is, of deep cloud containing both ice and liquid particles. The long-term mean optical depth error at the five locations spans the range 2–4, which we show to be small enough to allow calculation of top-of-atmosphere flux to within 10 % and surface flux to about 15 %.

scholarly journals Development of Embedded Boot Software for a Satellite Instrument Control Unit: Lessons Learned

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Jesús Fernández-Conde ◽  
Jaime Gómez-Saez-de-Tejada ◽  
David Pérez-Lizán ◽  
Rafael Toledo-Moreo
Keyword(s):  
Real Time ◽  
European Space Agency ◽  
Control Unit ◽  
Lessons Learned ◽  
System Failure ◽  
Application Software ◽  
Satellite Mission ◽  
Space Agency ◽  
Expected Performance ◽  
Instrument Control

A satellite spacecraft is generally composed of a central Control and Data Management Unit (CDMU) and several instruments, each one locally controlled by its Instrument Control Unit (ICU). Inside each ICU, the embedded boot software (BSW) is the very first piece of software executed after power-up or reset. The ICU BSW is a nonpatchable, stand-alone, real-time software package that initializes the ICU HW, performs self-tests, and waits for CDMU commands to maintain on-board memory and ultimately start a patchable application software (ASW), which is responsible for execution of the nominal tasks assigned to the ICU (control of the satellite instrument being the most important one). The BSW is a relatively small but critical software item, since an unexpected behaviour can cause or contribute to a system failure resulting in fatal consequences such as the satellite mission loss. The development of this kind of embedded software is special in many senses, primarily due to its criticality, real-time expected performance, and the constrained size of program and data memories. This paper presents the lessons learned in the development and HW/SW integration phases of a satellite ICU BSW designed for a European Space Agency mission.

scholarly journals Proposed standardized definitions for vertical resolution and uncertainty in the NDACC lidar ozone and temperature algorithms – Part 2: Ozone DIAL uncertainty budget

2016 ◽  
Vol 9 (8) ◽  
pp. 4051-4078 ◽  
Author(s):  
Thierry Leblanc ◽  
Robert J. Sica ◽  
Joanna A. E. van Gijsel ◽  
Sophie Godin-Beekmann ◽  
Alexander Haefele ◽  
...  
Keyword(s):  
Cross Sections ◽  
Stratospheric Ozone ◽  
Random Noise ◽  
Uncertainty Budget ◽  
Standard Uncertainty ◽  
Atmospheric Composition ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
Processing Chain ◽  
The Individual

Abstract. A standardized approach for the definition, propagation, and reporting of uncertainty in the ozone differential absorption lidar data products contributing to the Network for the Detection for Atmospheric Composition Change (NDACC) database is proposed. One essential aspect of the proposed approach is the propagation in parallel of all independent uncertainty components through the data processing chain before they are combined together to form the ozone combined standard uncertainty. The independent uncertainty components contributing to the overall budget include random noise associated with signal detection, uncertainty due to saturation correction, background noise extraction, the absorption cross sections of O3, NO2, SO2, and O2, the molecular extinction cross sections, and the number densities of the air, NO2, and SO2. The expression of the individual uncertainty components and their step-by-step propagation through the ozone differential absorption lidar (DIAL) processing chain are thoroughly estimated. All sources of uncertainty except detection noise imply correlated terms in the vertical dimension, which requires knowledge of the covariance matrix when the lidar signal is vertically filtered. In addition, the covariance terms must be taken into account if the same detection hardware is shared by the lidar receiver channels at the absorbed and non-absorbed wavelengths. The ozone uncertainty budget is presented as much as possible in a generic form (i.e., as a function of instrument performance and wavelength) so that all NDACC ozone DIAL investigators across the network can estimate, for their own instrument and in a straightforward manner, the expected impact of each reviewed uncertainty component. In addition, two actual examples of full uncertainty budget are provided, using nighttime measurements from the tropospheric ozone DIAL located at the Jet Propulsion Laboratory (JPL) Table Mountain Facility, California, and nighttime measurements from the JPL stratospheric ozone DIAL located at Mauna Loa Observatory, Hawai'i.

Design of internal quality control for reference value studies

2004 ◽  
Vol 42 (7) ◽  
Author(s):  
James O. Westgard
Keyword(s):  
Quality Control ◽  
Systematic Error ◽  
Total Error ◽  
Reference Value ◽  
Internal Quality Control ◽  
Internal Quality ◽  
Control Procedure ◽  
Graphical Tool ◽  
Critical Error ◽  
Power Curves

AbstractInternal quality control should assure that the desired quality goals are achieved during reference value studies. Quality goals are often stated in the form of allowable limits of error, such as an allowable total error or an allowable bias. For reference value studies, it may be more appropriate to utilize a goal for allowable bias. In either case, it is possible to calculate a metric in the form of the critical systematic error that can be used to guide selection or design of the internal quality control procedure. A graphical tool, called the critical-error graph, facilitates the selection by superimposing the calculated critical systematic error on the power curves of different control rules and numbers of control measurements. Examples are provided to illustrate the calculation of the critical systematic error from both an allowable total error goal and an allowable bias goal, using figures from an extensive tabulation of available total error and bias goals.

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