======================================================================================= Environment Canada's CrIS Fast Physical Retrieval (CFPR) Level 3 files ======================================================================================= The CrIS ammonia gridded level3 product is from the CrIS Fast Physical Retrieval (CFPR) level2 research product, therefore please work closely with the developers listed below as you analyze and use the data. Appropriate use of the data requires collaborating with the current developers, while feedback from users leads to a better product. If the data are used in a publication or presentation co-authorship is to be offered to the main developers. The data are to be used for research purposes and are provided as is without any express or implied warranties. The use of this data is subject to the Open Government License – Canada (https://open.canada.ca/en/open-government-licence-canada). The CrIS Fast Physical Retrieval (CFPR) ammonia datasets created by Environment and Climate Change Canada (Shephard et al., 2020) are publicly available at: https://hpfx.collab.science.gc.ca/~mas001/satellite_ext/cris with the level3 files at:https://hpfx.collab.science.gc.ca/~mas001/satellite_ext/cris/level3 The login information obtained by request from Mark Shephard. Mark Shephard Environment and Climate Change Canada 4905 Dufferin Street, Toronto, Ontario, Canada M3H 5T4 Mark.Shephard@ec.gc.ca Please refer to https://hpfx.collab.science.gc.ca/~mas001/satellite_ext/cris/CrIS_NH3_data_usage_statement.pdf for a detailed description of the ECCC CFPR Level2 product used as input files used to generate these gridded Level3 files. Selected References for the CrIS Fast Physical Retrievals (CFPR): White, E., M. W. Shephard, K. E. Cady-Pereira, S. Kharol, S. Ford, E. Dammers, E. Chow, N. Thiessen, D. Tobin, G. Quinn, J. O’Brien, J. Bash, Accounting for Non-detects in Satellite Retrievals: Application Using CrIS Ammonia Observations, Remote Sensing, 15, 2610, https://doi.org/10.3390/rs15102610, 2023. Shephard M. W., E. Dammers, K. E. Cady-Pereira, S. K. Kharol, J. Thompson, Y. Gainariu-Matz, J. Zhang, C. A. McLinden, A. Kovachik, M. Moran, S. Bittman, C. Sioris, D. Griffin, M. J. Alvarado, C. Lonsdale, V. Savic -Jovcic, and Q. Zheng, Ammonia measurements from space with the Cross-track Infrared Sounder (CrIS): characteristics and applications, Atmos. Chem. Phys., 20, 2277–2302, https://doi.org/10.5194/acp-20-2277-2020, 2020. Shephard, M.W. and K.E. Cady-Pereira, Cross-track Infrared Sounder (CrIS) Satellite Observations of Tropospheric Ammonia, Atmos. Meas. Tech., 8, 1323–1336, doi:10.5194/amt-8-1323-2015, 2015. ------------------------------------------------------------------------------------ Filename Structure: ------------------------------------------------------------------------------------ - The filename structure is: BeginningDate_EnddingDate_Region_DaynightFlag_GriddedDataType_Gridsize_Oversampling_Size_WeightThres_DayThres_level3.nc - The Dates are in the format: yyyymmdd - The Region is in the format of min_longitiude_max_longitude_min_latitude_max_latitude. The "n" refers to negative and the "p" refers to positive. The maximum longitude range goes from -180 to +180 from West to East, and the latitude range goes from -90 to + 90 from south to north. - The GriddedDataType is the gridded data in the files (e.g. total column, surface value); see examples below. - The other parameters in the filename are provided as global variables within the netcdf file, and defined below. ----------------------------------------------------------------------------------------- File Variables (Attributes are also in the netcdf files; can easily be viewed with tools such as ncdump -h on linux or unix system) ----------------------------------------------------------------------------------------- (Note: N = number of points, and poly = 4 (for the four corners of the grid boxes)) double Latitude(N) ; - Latitude of the centre of each grid box - Units: degrees (Max range: -90S to +90N) double Longitude(N) ; - Longitude of the centre of each grid box - Units: degrees (Max range: -180W to +180E) double polyLat(N, poly) ; - Latitude of the 4 corners of the each grid box - Units: degrees (+ for North and - for South: Max range: +90N to -90 S) double polyLon(N, poly) ; - Longitude of the 4 corners of each grid box - Units: degrees (+ for East and - for West: Max range:-180W to +180E ) double (N) ; - Gridded input Level2 (e.g. total column, surface nh3, etc.) for the time period specified in the filename - Used for diagnostics - types: see 'Gridded_Data Types' Section below - Units: units of gridded_data double _mad(N) ; - Gridded input Level2 (e.g. total column, surface nh3, etc.) for the time period specified in the filename - Used for diagnostics - Units: units of gridded_data double _median(N) ; - Gridded input Level2 (e.g. total column, surface nh3, etc.) for the time period specified in the filename - Used for diagnostics - Units: units of gridded_data double _sdev(N) ; - Gridded input Level2 (e.g. total column, surface nh3, etc.) for the time period specified in the filename - Used for diagnostics - Units: units of gridded_data double Filter_Mask(N) ; - Binary filter mask based on recommended spatial (wgt_thresh_perc) and temporal (day_thresh_perc) thresholds - Units: 0 : did not passed recommended filter test (these grid boxes should be filtered out) 1 : passed recommended filtering double N(N) ; - Number of total observations within the grid (Bin Points + Oversampled Points) - Units: unitless double N_Bin_Points(N) ; - Number of observations within the grid not including the oversampling region around the grid - Units: unitless double N_Dates(N) ; - Number of unique days with an observation within the grid including the surrounding oversample region. For example, a monthly gridded product in June would have a maximum of ~30 unique days. - Units: unitless double N_Oversampled_Points(N) ; - Number of observations within the grid that are only within the oversampling region (no bin points) - Units: unitless double Max_weight(N) ; - Maximum total weight for a gridded variable determined empirically assuming the specified weighting function (e.g. Gaussian) an even distribution of observations. - Units: unitless double Weight_Frac(N) ; - Ratio of the weight/Max_weight for each gridded value - Units: unitless double weight(N) ; - Sum of the weights used to compute each gridded value - Units: unitless ------------------------------------------------------------------------------------ File Global Attributes ------------------------------------------------------------------------------------ binsize ; - Grid spacing in degrees latitude and longitude (e.g. 0.1 is a 0.1x0.1 degree grid) of each gridded variable - Units: degrees oversample_binsize ; - Oversampling distance in degrees latitude and longitude outside of each gridded variable (e.g. 0.1 is a 0.1x0.1 degree grid considered in averaging around a grid box) - Units: degrees day_thresh_perc ; - Fraction of the number of unique days compared to the maximum potential days with observations. - For example, a specified threshold value of 0.2 would require for a monthly gridded product in June (with a maximum of 30 unique days) that there be at least 6 unique days within June that there were observations contributing to the gridded mean variable for the Mask_Filter=1. - Units: fraction (0 to 1) wgt_thresh_perc ; - Specified minimum weight ratio threshold required as part of a recommended Filter_Mask=1 for the gridded products. - Units: fraction (0 to 1) daynight_flag ; - Includes data only with specified daylight conditions. - types: night day daylight no daylight all: all data - Units: unitless min_quality_flag ; - Retrieval flag that excludes data less than specified flag value. - types: -1:did not converge >=1: converged >=2: large outlier flag >=3: Retrieaval quality flag >=4: Convervative retrieval quality flag >=5: same as 4 with min DOFS of 0.1. - Units: unitless reject_cloud_flag: - List of rejected data due to specified cloud parameters. - types: 1: rejects cloudy retrievals 3: rejects non-detects - Units: unitless Note: The day_thresh_perc and wgt_thresh_perc above only get used to compute the Filter_Mask(N), which the user can use to filter the gridded data if desired. They have not been previously applied to the gridded data. ------------------------------------------------------------------------------------ Potential Gridded_Data Types (see filename): ------------------------------------------------------------------------------------ xretv: - Gridded surface level ammonia values - Units: ppbv tot_col: - Gridded total column ammonia values - Units: molec/cm2 tsfc: - Gridded surface temperature - Units: K DOF: - Degrees of freedom for signal - Units: unitless