# Invisible tracks archive
This stores collocated shipping trajectory and MODIS cloud product data in the CEDA archive.

The code used to produce this dataset can be found under DOI: 10.5281/zenodo.6556425 
This data was used for the upcoming publication: Manshausen et al., 2022, Invisible Ship Tracks Show Large Cloud Sensitivity to Aerosol, Nature (accepted).

The data describes cloud properties in areas that we estimate to be polluted by ships. We found these locations by advecting shipping emissions with the winds from reanalysis data. The data also includes comparison data from locations next to the shipping-polluted tracks. This is referred to as, e.g. r_eff for the polluted, r_eff_1 and r_eff_3 for the upolluted clouds below. The data is organised by month into individual csv files.

## Data sources
Data comes from Emission gridmaps produced from AIS data, ERA5 reanalysis data (Hersbach et al., 2020, The ERA5 global reanalysis), as well as the MODIS L2 cloud product (Platnick et al., 2003, The MODIS cloud products).

## Method 
An in-depth description of the Method will follow in the upcoming publication. For a technical overview, see the code cited above.

## Data variables 

For variables 1-7, as well as 14, there are three records, variable, variable_1, variable_3. Here, variable_1 and variable_3 are the counterfactual, non-polluted retrievals. variable_1 is always south-west from the polluted region (variable), variable_3 always to the north-east.

0. unnamed/index column:    date and time of the emission
1. 'latitude':              latitude of emissions advected until the overpass time of the MODIS satellite 
2. 'longitude':             longitude of emissions advected until the overpass time of the MODIS satellite
3. 'r_eff':                 cloud droplet effective radius from MODIS 06 L2 cloud product
4. 'npoints':               number of retrieved pixels for this location
5. 'LWP':                   liquid water path from MODIS 06 L2 cloud product
6. 'COT':                   cloud optical thickness from MODIS 06 L2 cloud product
7. 'CTH':                   cloud top temperature from MODIS 06 L2 cloud product
8. 'signal':                emission signal of the ship at this time   
9. 'overpass':              overpass time of the MODIS satellite
10. 'particle':             tracking ID of the ship
11. 'terra':                whether the cloud measurements come from MODIS Terra (if False, they come from Aqua)
12. 'EIS':                  ERA5-EIS collocated to the advected position at the time of overpass
13. 'ocean':                whether the location is over the ocean
14. 'Nd':                   cloud droplet number concentration, calculated from COT and r_eff
15. 'chil', 'azor', 'cver','ango':  bools for whether the location corresponds to the regions of interest in the Chilean and Angolan Stratocumulus or the Azores or Cabo Verde Cumulus
16. 'hours_diff':           difference in hours (rounded down) between the emission time and the overpass time


## Usage
To open and analyse these files, we recommend the use of the pandas (for single files) and dask (for several years) libraries.