Climate Data Records from Meteosat First Generation Part III: Recalibration and Uncertainty Tracing of the Visible Channel on Meteosat-2–7 Using Reconstructed, Spectrally Changing Response Functions
<p>The MVIRI uncertainty diagram illustrates the effects that contribute to the uncertainties of the different parameters of the measurement equation. Note that the measurement equation here is Equation (1) where the calibration coefficient <math display="inline"><semantics> <mrow> <msub> <mi>a</mi> <mrow> <mi>c</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics></math> is expanded by Equation (10). Notation is explained in the text.</p> "> Figure 2
<p>Spectral Response functions of Meteosat-2-7 plotted together with SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) spectra acquired during 2002 at three target sites. (<b>a</b>) shows the spectra measured by SCIAMACHY at the Algeria site, (<b>b</b>) shows the spectra measured at the Nile-delta and the (<b>c</b>) shows those measured at the Atlantic-1 site. Spectra are plotted at in transparent black to better illustrate their spread. Spectra with strong cloud contamination were removed before plotting (see <a href="#sec3dot9dot1-remotesensing-11-01165" class="html-sec">Section 3.9.1</a>). Note that for band-adjustment/homogenisation more sophisticated filtering regarding clouds and scene heterogeneity is applied (<a href="#sec3dot9dot1-remotesensing-11-01165" class="html-sec">Section 3.9.1</a>).</p> "> Figure 3
<p>Scan pattern of one SCIAMACHY overpass over Algeria-3 with 4 pixel per scanline. The numbers provide the viewing zenith angle at the center of each pixel. The green box is the 2° × 2° box of the target site. The red pixel are considered for the computation of the spectral band adjustment factor for the homogenisation of the timeseries at this target. The orange pixel are disregarded.</p> "> Figure 4
<p>Mean SCIAMACHY spectrum collected above the Algeria-3 validation site along with the spectral response functions of the VIS channel on Meteosat-7 and the HRVIS channel on MSG1.</p> "> Figure 5
<p>Convoluted clear-sky SCIAMACHY spectra above Algeria-3 using Meteosat-2 and Meteosat-5 SRFs that were valid at each satellites’ launch date.</p> "> Figure 6
<p>Illustration of the approach for the MVIRI/SEVIRI comparison. Site-specific spectral band adjustment functions between the two MVIRI datasets and the SEVIRI HRVIS band are computed based on SCIAMACHY spectra that are collected during a five-month period. The five-month period envelops the one-month period during which the actual MVIRI and SEVIRI data are collected that are displayed in the histograms.</p> "> Figure 7
<p>Locations of the areas considered for finding potentially ray-matched SCIAMACHY-MVIRI collocations (Zero Degree Mission (ZDM) and Indian Ocean data coverage (IODC)) that are exploited in this study. The collocation results for each area are presented in Figure 16.</p> "> Figure 8
<p>Expected time series at Algeria-3 and Atlantic-1 based on representative mean SCIAMACHY spectra (<a href="#remotesensing-11-01165-f002" class="html-fig">Figure 2</a>) that are convoluted with the pre-launch SRFs (old) and with the time-variant, reconstructed SRFs (new). Grey shading is the uncertainty of the reflectance computed from the uncertainty provided along with the SRFs.</p> "> Figure 9
<p>Harmonised MVIRI VIS fundamental climate data records (FCDR) time series of clear-sky reflectance at Algeria-3 along with structured and independent uncertainties. Trends and jumps are due to the changing SRFs. Alternating measurements from two satellites, as in 1992, are mostly due to a takeover by the backup satellite during maintenance operations of the primary satellite.</p> "> Figure 10
<p>Harmonised MVIRI VIS FCDR time series of clear-sky reflectance at Atlantic-1 along with structured and independent uncertainties. Trends and jumps are due to the changing SRFs. Alternating measurements from two satellites, as in 1992, are mostly due to a takeover by the backup satellite during maintenance operations of the primary satellite.</p> "> Figure 11
<p>Homogenised time series of recalibrated broadband reflectances at Algeria-3, Nile-delta and Atlantic-1.</p> "> Figure 12
<p>Anomalies of the homogenised reflectance time series and their trends. Anomalies are the deviation from the mean annual reflectance cycles. Additional filtering for cloud contamination was applied. The filter computes the 25th percentile from a rolling kernel of 30 days around each reflectance measurement. Measurements that are brighter than this value are rejected in order to display only measurements that are certainly cloud free. Note that for the Atlantic site the periods with globally elevated aerosol loads due to volcanic eruptions are excluded from the stability analysis.</p> "> Figure 13
<p>Histogram of SEVIRI HRVIS plotted as reference together with the histograms of the operational MVIRI dataset and the recalibrated MVIRI FCDR, as obtained from cloud-free Algeria-3 pixels at 12:00 UTC slots during March 2005. The MVIRI datasets are band adjusted to the SRF of the SEVIRI HRVIS band according to the given Spectral Band Adjustment Factors (SBAFs). The SBAFs are computed on the same set of SCIAMACHY spectra and the difference between both SBAFs is entirely due to the different shapes of the SRFs in the operational and the FCDR dataset.</p> "> Figure 14
<p>Histogram of SEVIRI HRVIS plotted as reference together with the histograms of the operational MVIRI dataset and the recalibrated MVIRI FCDR, as obtained from entirely cloud-covered pixels at 12:00 UTC slots during March 2005. Clouds are classified into high clouds (<b>a</b>), middle clouds (<b>b</b>) and low clouds (<b>c</b>). The MVIRI datasets were band adjusted to the SRF of the SEVIRI HRVIS band according to the given SBAFs. For each cloud-class the SBAFs for the operational dataset and for the FCDR are computed on the same set of SCIAMACHY spectra and the difference between both SBAFs is entirely due to the different shapes of the SRFs in the operational dataset and the FCDR.</p> "> Figure 15
<p>Histogram of SEVIRI HRVIS plotted as reference together with the histograms of the operational MVIRI dataset and the recalibrated MVIRI FCDR, as obtained from cloud-free Atlantic-1 pixels at 12:00 UTC slots during March 2005. The MVIRI datasets were band adjusted to the SRF of the SEVIRI HRVIS band according to the given SBAFs. The SBAFs are computed on the same set of SCIAMACHY spectra and the difference between both SBAFs is entirely due to the different shapes of the SRFs in the operational and the FCDR dataset.</p> "> Figure 16
<p>Collocations between SCIAMACHY and MVIRI onboard MET7 for (<b>a</b>) Atlantic-west, (<b>b</b>) Atlantic-east and (<b>c</b>) Kenya. Collocations between SCIAMACHY and MET5 are provided in (<b>d</b>) for Somalia. Grey marks stand for the dataset with the pre-launch SRF characterisation. Blue crosses stand for the harmonised/recalibrated FCDR. The collocations are constrained to relative azimuth angles between the two instruments of 5°, to zenith angle differences of 15° and to acquisition time differences of 5 min. Only collocations with MVIRI standard deviation of below 0.12 within a SCIAMACHY pixel are considered. Over the Atlantic areas and the Somalian area collocations were acquired from data collected during 2002–2006, whereas data collected during 2006–2010 were used for the collocations over the Kenyan area.</p> "> Figure 17
<p>Spectral characteristics of the collocation regions and of Algeria-3 collected during 10 days of February 2005. In order to emphasise on cloud-free surfaces a set of 10% of the darkest spectra was averaged for each region. For the Atlantic site also a set of the 10% brightest spectra was averaged to illustrate the spectral shape of cloudy observations. The grey shading indicates the standard deviation of each set.</p> ">
Abstract
:1. Introduction
2. Measurements
2.1. MVIRI VIS Observations
- The pre-operational period with Meteosat-1 (launch: 23/11/1977), Meteosat-2 (launch: 10/06/1981) and Meteosat-3 (launch: 15/06/1988)
- The slightly improved Meteosat Operational Program (MOP) Meteosat-4 (launch: 19/04/1989), Meteosat-5 (launch: 02/03/1991) and Meteosat-6 (launch: 20/11/1993)
- The Meteosat Transition Program (MTP) with Meteosat-7 (launch: 03/09/1997) which benefitted from an enhanced pre-flight characterisation of the radiometer.
2.2. SEVIRI Measurements
2.3. SCIAMACHY Measurements
3. Methods
3.1. Measurement Equation
3.2. Noise of the Earth Counts
3.3. Uncertainties of the Dark Signal Offset (Space Count)
3.4. Uncertainties of the Recalibration Parameters
3.5. Uncertainty of the Solar Irradiation
3.6. Uncertainty of the Solar Zenith Angle
3.7. Combination of Independent Uncertainty Effects
3.8. Combination of Structured Uncertainty Effects
3.9. Validation Methodology
- Evaluation of harmonised and homogenised time-series (Section 3.9.1)
- Comparison against SEVIRI observations (Section 3.9.2)
- Comparison against SCIAMACHY observations (Section 3.9.3)
3.9.1. Evaluation of Harmonised and Homogenised Time Series
Spectral Band Adjustment (Homogenisation)
Assessment of Decadal Stability
3.9.2. Comparisons with SEVIRI
3.9.3. Collocations with SCIAMACHY
4. Results and Discussion
4.1. Evaluation of Harmonised Time Series
4.2. Evaluation of Homogenised Time Series
4.3. Case-Study Comparison with SEVIRI
4.4. Collocations with SCIAMACHY
5. Summary and Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Abbreviations
AVHRR | Advanced Very High Resolution Radiometer |
CDR | Climate Data Records |
EUMETSAT | European Organisation for the Exploitation of Meteorological Satellites |
FCDR | Fundamental Climate Data Records |
FIDUCEO | FIDelity and Uncertainty in Climate data records from Earth Observation |
GSICS | Global Space-based Inter-calibration System |
IR | Infrared |
MFG | Meteosat First Generation |
MSG | Meteosat Second Generation |
MVIRI | Meteosat Visible Infra-Red Imager |
NOAA | National Oceanic and Atmospheric Administration |
SBAF | Spectral Band Adjustment Factor |
SCIAMACHY | SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY |
SEVIRI | Spinning Enhanced Visible Infra-Red Imager |
SNO | Simultaneous Nadir Overpas |
SRF | Spectral Response Function |
SZA | Satellite zenith angle |
VZA | Viewing zenith angle |
VAA | Viewing azimuth angle |
VIS | Visible |
WMO | World Meteorological Organization |
WV | Water Vapor |
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Channel | Sampling Nadir (km) | Nominal Spectral Band (μm) |
---|---|---|
VIS 0.7 | 2.25 | 0.40–1.10 |
WV 6.4 | 4.5 | 5.70–7.10 |
TIR 11.5 | 4.5 | 10.5–12.5 |
Channel | Sampling Nadir (km) | Nominal Spectral Band (μm) | Mission Requirement on SNR @1% Albedo |
---|---|---|---|
VIS 0.6 | 3 | 0.56–0.71 | 10.1 |
VIS 0.8 | 3 | 0.74–0.88 | 7.28 |
NIR1.6 | 3 | 1.50–1.78 | 3.0 |
HRVIS | 1 | 0.37–1.25 | 4.3 |
Component | Error Correlation | Justification |
---|---|---|
Intrinsic RTM uncertainty | Not correlated | Depends on illumination geometry which is different for each 5-day run due to different sets of discarded observations (e.g., due to cloudiness). |
Surface characterisation uncertainty | Not correlated | The calibration includes up to 18 desert targets each having its own surface characterisation. The number and weighting the targets varies from 5-day run to 5-day run (e.g., due to cloudiness). |
Atmosphere characterisation uncertainty | Not correlated | A systematic bias of the atmosphere parameterisation across the 18 different target sites and multiple days is assumed unlikely. |
Spectral Response Function (SRF) uncertainty | Entirely correlated in time and between wavelengths | The SRF characterisation algorithm is performed once per satellite and therefore entirely correlated among all 5-day runs for a satellite. |
Site | Land Cover Type | Dominant Spectral Contribution | Central Latitude | Central Longitude | Size of Box | thr1 | thr2 | thr3 | thr4 |
---|---|---|---|---|---|---|---|---|---|
Algeria-3 | Desert | Red | 30.32 | 7.66 | 2° × 2° | 0.47 | 0.38 | 15 | 0.5 |
Nile | Agricultural land | Green | 30.5 | 31.25 | 0.5° × 0.5° | 0.35 | 0.35 | 20 | 0.03 |
Atlantic-1 | Sea | Blue | −22.5 | 9.5 | 2° × 2° | 0.02 | 0.053 | 5 | 0.02 |
Test | Condition | Rationale |
---|---|---|
1 | Cloud rejection: Radiance between 1120 nm and 1150 nm is subject of H20 absorption. Clouds reduce the H2O absorption path through the atmosphere and therefore increase this ratio. | |
2 | Cloud rejection: The reflectance is convoluted with the spectral response function of the instrument that is the reference for the band-adjustment. Cloud contamination increases the convoluted reflectance in the VIS range. | |
3 | Only SCIAMACHY observations with viewing geometries that are comparable to MVIRI geometries are considered. Here β denotes the scattering angles of both SCIAMACHY and MVIRI as computed according to Equation (14). | |
4 | Only SCHIAMACHY observations with low scene heterogeneity are considered in order to avoid inconsistencies of the band adjustment due to remaining clouds or unwanted surface features. |
Site | Criterion | Central Latitude | Central Longitude | Size of Box (lat × lon) |
---|---|---|---|---|
Algeria-3 | Cloud fraction < 0 | 30.32 | 7.66 | 4° × 4° |
High-cloud | Cloud-top-pressure < 200 hPa | 0.0 | 0.0 | 10° × 10° |
Mid-cloud | Cloud-top-pressure 200–700 hPa | 0.0 | 0.0 | 10° × 10° |
Low-cloud | Cloud-top-pressure >700 hPa | 0.0 | 0.0 | 10° × 10° |
Atlantic-1 | Cloud fraction < 0 | −22.5 | 9.5 | 10° × 5° |
Location | Central Lat | Central Lon | Surface | Monitored | VZA SCIAM | VAA SCIAM |
---|---|---|---|---|---|---|
Atlantic-west | 4.5 | −20 | Sea | MET7 ZDM | ~26.7 | ~102.5 |
Atlantic-east | 1.5 | −6 | Sea | MET7 ZDM | ~8.8 | ~102.5 |
Kenya | 5.5 | 37 | Semidesert | MET7 IODC | ~26.7 | ~102.5 |
Somalia | 5.5 | 41 | Semidesert | MET5 IODC | ~26.7 | ~102.5 |
Site | Site Mean Reflectance | Stability of Reflectance | Fraction of Site Mean |
---|---|---|---|
[reflectance decade−1] | [%] | ||
Algeria-3 | 0.36 ± 0.02 | −0.0020 ± 0.000 | −0.54 ± 0.02 |
Nile | 0.18 ± 0.03 | 0.0012 ± 0.000 | 0.66 ± 0.03 |
Atlantic-1 | 0.05 ± 0.00 | 0.0027 ± 0.000 | 5.26 ± 0.01 |
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Share and Cite
Rüthrich, F.; John, V.O.; Roebeling, R.A.; Quast, R.; Govaerts, Y.; Woolliams, E.R.; Schulz, J. Climate Data Records from Meteosat First Generation Part III: Recalibration and Uncertainty Tracing of the Visible Channel on Meteosat-2–7 Using Reconstructed, Spectrally Changing Response Functions. Remote Sens. 2019, 11, 1165. https://doi.org/10.3390/rs11101165
Rüthrich F, John VO, Roebeling RA, Quast R, Govaerts Y, Woolliams ER, Schulz J. Climate Data Records from Meteosat First Generation Part III: Recalibration and Uncertainty Tracing of the Visible Channel on Meteosat-2–7 Using Reconstructed, Spectrally Changing Response Functions. Remote Sensing. 2019; 11(10):1165. https://doi.org/10.3390/rs11101165
Chicago/Turabian StyleRüthrich, Frank, Viju O. John, Rob A. Roebeling, Ralf Quast, Yves Govaerts, Emma R. Woolliams, and Jörg Schulz. 2019. "Climate Data Records from Meteosat First Generation Part III: Recalibration and Uncertainty Tracing of the Visible Channel on Meteosat-2–7 Using Reconstructed, Spectrally Changing Response Functions" Remote Sensing 11, no. 10: 1165. https://doi.org/10.3390/rs11101165