“Consistency and quality assessment of the Metop-A/IASI and Metop-B/IASI operational trace gas products (O3, CO, N2O, CH4and CO2) in the Subtropical North Atlantic”, paper published in AMTD

In the framework of the Spanish project NOVIA (Towards a Near Operational Validation of IASI level 2 trace gas products), this paper presents the tools and methodology for performing a routine comprehensive monitoring of consistency and quality of IASI (Infrared Atmospheric Sounding Interferometer) trace gas Level 2 (L2) products (O₃, CO, N₂O, CH₄ and CO₂) generated at EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) using ground-based observations at the Izaña Atmospheric Observatory (IZO, Tenerife). As a demonstration the period 2010-2014 was analysed, covering the version 5 of the IASI L2 processor.
Firstly, we assess the consistency between the total column (TC) observations from the IASI sensors on-board the EUMETSAT Metop-A and Metop-B meteorological satellites (IASI-A and IASI-B, respectively) in the subtropical North Atlantic region during the first two years of IASI-B operations (2012-2014). By analysing different time scales, we probe the daily and annual consistency of the variability observed by IASI-A and IASI-B and, thereby, assess the suitability of IASI-B for continuation of the IASI-A time series. The continuous inter-comparison of both IASI sensors also offers important diagnostics for identifying inconsistencies between the data records and for documenting their temporal stability.
Once the consistency of IASI sensors is documented we estimate the overall accuracy of all the IASI trace gas TC products by comparing to coincident ground-based Fourier Transform Infrared Spectrometer (FTS) measurements performed at IZO from 2010 to 2014. The IASI L2 products reproduce the ground-based FTS observations well at the longest temporal scales, i.e., annual cycles and long-term trends for all the trace gases considered (Pearson correlation coefficient, R, larger than 0.95 and 0.75 for long-term trends and annual cycles, respectively, see Figure 1) with the exception of CO₂. For CO₂ acceptable agreement is only achieved for long-term trends (R~0.70). The differences observed between IASI and FTS observations can be in part attributed to the different vertical sensitivities of the two remote sensing instruments and also to the degree of maturity of the IASI products: O₃ and CO are pre-operational, while N₂O, CH₄ and CO₂ are, for the period covered by this study, aspirational products only and are not considered mature. Regarding shorter timescales (single or daily measurements), only the O₃ product seems to be show good sensitivity to actual atmospheric variations (R~0.80), while the CO product is only moderately sensitive (R~0.50). For the remainder of the trace gases, further improvements would be required to capture the day-to-day real atmospheric variability.

Figure 1. Pearson correlation coefficient (upper panel), between IASI-A and FTS observations for all the trace gases considered at different time scales: single measurements (de-trended + de-seasonalised variability within ±1 h, Det + Des 1 h), daily (de-trended + de-seasonalised variability within the same day, Det + Des Day), annual, and long-term trend. Bottom panel shows the same, but for the standard deviation [in %] of the corresponding differences. The solid black lines represent the day-to-day variability calculated from the FTS observations at IZO between 2010 and 2014.

For more details about this work please refer to: García, O. E., Sepúlveda, E., Schneider, M., Hase, F., August, T., Blumenstock, T., Kühl, S., Munro, R., Gómez-Peláez, A., Hultberg, T., Redondas, A., Barthlott, S., Wiegele, A., González, Y., and Sanromá, E.: Consistency and quality assessment of the Metop-A/IASI and Metop-B/IASI operational trace gas products (O3, CO, N2O, CH4 and CO2) in the Subtropical North Atlantic, Atmos. Meas. Tech. Discuss., 8, 13729-13778, doi:10.5194/amtd-8-13729-2015, 2015, http://www.atmos-meas-tech-discuss.net/8/13729/2015/amtd-8-13729-2015.html.