Release Note of Bias-corrected FTS SWIR Level 2 CH 4 Product (V02.75) for General Users

Transcription

1 Release Note of Bias-corrected FTS SWIR Level 2 CH 4 Product (V02.75) for General Users February 28, 2019 NIES GOSAT Project 1. Introduction The NIES GOSAT Project has produced the FTS SWIR Level 2 CH 4 products (hereinafter referred to as SWIR L2 CH 4 product ) from the FTS Level 1B products (hereinafter referred to as FTS L1B data ) provided from JAXA. The SWIR L2 CH 4 products (V02.72) with the FTS L1B data (V ) as the input data during the observation period from April 23, 2009 to November 24, 2018, have been released to General Users (GU). Using the ground-based observation data of the Total Carbon Column Observation Network (TCCON), bias-corrections are conducted on the column amounts of methane (XCH 4 ) of the SWIR L2 CH 4 products (V02.72), and the results are released as the bias-corrected FTS SWIR Level 2 CH 4 products (hereinafter referred to as corrected SWIR L2 CH 4 product ) (V02.75). The observation period from April 23, 2009 to November 24, 2018 is covered. 2. Match-up between SWIR L2 CH 4 product and TCCON data We selected the TCCON data corresponding to the observation time and the observation position of each FTS scan stored in the SWIR L2 CH 4 product from 2009 to 2016 under the following criteria (This selection is called match-up ): (1) Select the FTS scan with the center position of the FTS IFOV within 2 degrees (land with Gain-H) or 5 degrees (land with Gain-M and ocean with Gain-H/M) from the latitude and longitude of the TCCON site depending on the observation area (land and ocean) and the observation gain (H and M) of the FTS, and with the difference between the average altitude of the FTS IFOV and the elevation of the TCCON site within 0.5 km (land with Gain-H and ocean with Gain-H/M) or 2 km (land with Gain-M); (2) Select the data of the TCCON site located at the shortest distance from the center position of the FTS IFOV; (3) Calculate the mean value of the TCCON data within 30 minutes before and after the observation time of the FTS scan. The TCCON data can be obtained from the TCCON Data Archive website. However, they are updated irregularly and may be different depending on the acquisition time. Table 2-1 is the list of the TCCON data referenced in the bias-correction processing. The FTS scan numbers of match-up results for land and ocean with each observation gain are shown in Tables 2-2 respectively, where the land fraction within FTS IFOV of 100% is defined as land and 0% as ocean ; the mixed areas of 60% or more and less than 100% are excluded

2 Table 2-1: TCCON data referenced in bias-correction processing Site Lat. Lon. Elev. Site name code (deg. N) (deg. E) (km) File name ae Ascension Island ae _ public.nc an Anmyeondo an _ public.nc bi Białystok bi _ public.nc br Bremen br _ public.nc ci Pasadena ci _ public.nc db Darwin db _ public.nc df Edwards df _ public.nc et East Trout Lake et _ public.nc fc Four Corners fc _ public.nc gm Garmisch gm _ public.nc if Indianapolis if _ public.nc iz Izaña iz _ public.nc jc JPL jc _ public.nc jf JPL jf _ public.nc js Saga js _ public.nc ka Karlsruhe ka _ public.nc lh Lauder (120HR) lh _ public.nc ll Lauder ll _ public.nc ma Manaus ma _ public.nc oc Lamont oc _ public.nc or Orléans or _ public.nc pa Park Falls pa _ public.nc pr Paris pr _ public.nc ra Reunion Island ra _ public.nc rj Rikubetsu rj _ public.nc so Sodankylä so _ public.nc sp Ny-Ålesund sp _ public.nc tk Tsukuba tk _ public.nc wg Wollongong wg _ public.nc zs Zugspitze zs _ public.nc - 2 -

3 Table 2-2: Match-up FTS scan number of SWIR L2 CH 4 product [ ] Site Land Ocean Site name code Gain H Gain M Gain H Gain M ae Ascension Island an Anmyeondo bi Białystok br Bremen ci Pasadena 1, db Darwin df Edwards 98 1, et East Trout Lake fc Four Corners gm Garmisch if Indianapolis iz Izaña jc JPL jf JPL js Saga ka Karlsruhe lh Lauder (120HR) ll Lauder ma Manaus oc Lamont 1, or Orléans pa Park Falls pr Paris ra Reunion Island rj Rikubetsu so Sodankylä sp Ny-Ålesund tk Tsukuba wg Wollongong zs Zugspitze Total 5,171 1,688 1,

4 3. Method of bias-correction 3.1 Multiple regression analysis Based on the match-up results between the SWIR L2 CH 4 product and the TCCON data from 2009 to 2016, the multiple regression analyses were performed on XCH 4 by categories of land (Gain H and Gain M) and ocean (Gain H), using the following regression equation, which includes same explanatory variables as the multiple regression analyses of the column amounts of carbon dioxide (XCO 2 ) 1). The parameters used for the explanatory variables in this regression equation are shown in Table 3-1. For each explanatory variable, the deviation from the mean value of all match-up FTS scans was used. XCH Bias corrected 4 =XCH 4 +C 1 (AOT ) AOT +C 2 (ΔP S ΔP )+C3 S (Airmass ) Aırmass +C 4 (Albedo_O 2 Albedo_O )+C5 2 The errors (variance σ 2 ) of the bias-corrected XCH 4 were calculated by the following equation. (σxch 4 Bias corrected ) 2 =(σxch 4 smoothing_error ) 2 +(σxch 4 retrieval_noise ) 2 +(σxch interference_error 4 ) 2 +σ 2 1 (AOT )2 AOT +σ 2 2 (ΔP S ΔP )2 2 S +σ3 (Airmass )2 Aırmass +σ (Albedo_O 2 Albedo_O )2 2 +σ5 For land (Gain H and Gain M), the multiple regression analyses were performed considering the weight corresponding to the match-up FTS scan number of each TCCON site. For ocean (Gain H), however, the weight was not considered. 3.2 Bias-correction processing We conducted comprehensive bias-correction processing using this multiple regression analyses results. The differences in XCH 4 between the SWIR L2 CH 4 product and the TCCON data, the partial regression coefficients and the intercept obtained by these multiple regression analyses, and the differences in XCH 4 between the corrected SWIR L2 CH 4 product and the TCCON data are summarized in Tables 3-2. Note that the empirical bias-correction processing using the multiple regression analyses results of the land (Gain H and Gain M) are also applied to the FTS scans of the mixed areas (land fraction within FTS IFOV of 60% or more and less than 100%), respectively. The empirical bias-correction processing using the multiple regression analyses results of the ocean (Gain H) is applied to the FTS scans of the ocean (Gain M). Furthermore, we apply the biascorrection processing determined from the match-up results from 2009 to 2016 to the FTS scans of the SWIR L2 CH 4 product after 2017, and produce and release the corrected SWIR L2 CH 4 product. Tables 3-3 and 3-4 summarize these bias-correction processing results for 2017 and The scatter diagrams of XCH 4 over land (Gain H and Gain M) and ocean (Gain H) between the SWIR L2 CH 4 product and the TCCON data, the corrected SWIR L2 CH 4 product and the TCCON data from 2009 to 2016, 2017, and 2018 are shown separately for land (Gain H and Gain M) and ocean (Gain H) in Figures 3-1 to

5 Table 3-1: Parameters used for explanatory variables in regression equation (XCH 4 ) Parameter Description Land Ocean Gain H Gain M Gain H AOT Aerosol optical thickness retrieved simultaneously by FTS SWIR L2 processing ΔP S Difference between surface pressure retrieved simultaneously by FTS SWIR L2 processing and a priori surface pressure Airmass Airmass calculated by 1/cos (Solar zenith angle) + 1/cos (Satellite zenith angle) Albedo_O 2 Surface albedo of O 2 A-band retrieved simultaneously by FTS SWIR L2 processing - Table 3-2: Multiple regression analyses and bias-correction processing results of SWIR L2 CH 4 product (XCH 4 ) [ ] Land Ocean Gain H Gain M Gain H Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data C 1 (10-3 ppm) Partial regression C 2 (10-3 ppm/hpa) coefficient C 3 (10-3 ppm) C 4 (10-3 ppm) Multiple Intercept C 5 (10-3 ppm) regression σ 1 (10-3 ppm) analysis SD of partial regression σ 2 (10-3 ppm/hpa) coefficient σ 3 (10-3 ppm) σ 4 (10-3 ppm) SD of intercept σ 5 (10-3 ppm) Adjusted R-square Corrected Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data

6 Table 3-3: Bias-correction processing results of SWIR L2 CH 4 product (XCH 4 ) [2017] Land Ocean Gain H Gain M Gain H Match-up FTS scan number (Total of each TCCON site) Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data Corrected Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data Table 3-4: Bias-correction processing results of SWIR L2 CH 4 product (XCH 4 ) [2018] Land Ocean Gain H Gain M Gain H Match-up FTS scan number (Total of each TCCON site) Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data Corrected Mean difference from TCCON data (10-3 ppm) SWIR L2 SD of difference from TCCON data (10-3 ppm) CH 4 product Correlation coefficient with TCCON data Note: The latest TCCON data obtained in February 2019 were used for the match-up in Tables 3-3 and 3-4, and Figures 3-4 to 3-9 (Table 3-5, red files are updated from Table 2-1)

7 Table 3-5: TCCON data used in match-up for 2017 and 2018 Site Lat. Lon. Elev. Site name code (deg. N) (deg. E) (km) File name ae Ascension Island ae _ public.nc an Anmyeondo an _ public.nc bi Białystok bi _ public.nc br Bremen br _ public.nc ci Pasadena ci _ public.nc db Darwin db _ public.nc df Edwards df _ public.nc et East Trout Lake et _ public.nc fc Four Corners fc _ public.nc gm Garmisch gm _ public.nc if Indianapolis if _ public.nc iz Izaña iz _ public.nc jc JPL jc _ public.nc jf JPL jf _ public.nc js Saga js _ public.nc ka Karlsruhe ka _ public.nc lh Lauder (120HR) lh _ public.nc ll Lauder ll _ public.nc ma Manaus ma _ public.nc oc Lamont oc _ public.nc or Orléans or _ public.nc pa Park Falls pa _ public.nc pr Paris pr _ public.nc ra Reunion Island ra _ public.nc rj Rikubetsu rj _ public.nc so Sodankylä so _ public.nc sp Ny-Ålesund sp _ public.nc tk Tsukuba tk _ public.nc wg Wollongong wg _ public.nc zs Zugspitze zs _ public.nc - 7 -

8 Figure 3-1: Scatter diagrams of XCH 4 over land (Gain H) with TCCON data [ ] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75) - 8 -

9 Figure 3-2: Scatter diagrams of XCH 4 over land (Gain M) with TCCON data [ ] (Top: SWIR L2 product CH 4 V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75) - 9 -

10 Figure 3-3: Scatter diagrams of XCH 4 over ocean (Gain H) with TCCON data [ ] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

11 Figure 3-4: Scatter diagrams of XCH 4 over land (Gain H) with TCCON data [2017] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

12 Figure 3-5: Scatter diagrams of XCH 4 over land (Gain M) with TCCON data [2017] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

13 Figure 3-6: Scatter diagrams of XCH 4 over ocean (Gain H) with TCCON data [2017] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

14 Figure 3-7: Scatter diagrams of XCH 4 over land (Gain H) with TCCON data [2018] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

15 Figure 3-8: Scatter diagrams of XCH 4 over land (Gain M) with TCCON data [2018] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

16 Figure 3-9: Scatter diagrams of XCH 4 over ocean (Gain H) with TCCON data [2018] (Top: SWIR L2 CH 4 product V02.72, Bottom: Corrected SWIR L2 CH 4 product V02.75)

17 Reference 1) NIES GOSAT Project (2018), Release Note of Bias-corrected FTS SWIR Level 2 CO 2 Product (V02.75) for General Users, _en.pdf. Acronyms AOT FTS GOSAT IFOV JAXA NIES SD SWIR Aerosol Optical Thickness Fourier Transform Spectrometer Greenhouse gases Observing SATellite Instantaneous Field Of View Japan Aerospace Exploration Agency National Institute for Environmental Studies Standard Deviation Short-Wavelength Infrared