# Description:
Gridded dataset of rainfall intensities (mm/h) covering Sri Lanka over the period 12 September 2019 through 31 December 2019. Commercial microwave link (CML) data were used to estimate path-average rainfall between telephone towers. These were interpolated to 15-min rainfall maps on a 0.02 degree grid (approximately 4 km). The employed CML data were minimum and maximum received signal levels (almost all vertically polarized) over 15-min intervals, based on 6 samples in a minute, with a power resolution of 0.1 dB and with transmitted signal levels assumed to be constant. CML data from on average 1140 link paths were employed, being part of the network from Dialog Sri Lanka, one of the mobile network operators in Sri Lanka. After initial quality control of CML data, the open-source R package RAINLINK version 1.2 (https://github.com/overeem11/RAINLINK) was employed, including wet-dry classification and outlier filter, to compute mean 15-min path-averaged rainfall intensities. RAINLINK's default parameter settings (Overeem et al, 2016), which have been optimized for the Netherlands, were used. RAINLINK's interpolation algorithm ordinary Kriging was used to obtain 15-min rainfall maps employing the following climatological spherical variogram model parameters: nugget of 0.370299 mm^2, sill of 3.70299 mm^2 and range of 18.66113 km. These are the values from the Netherlands representative for 10 August and based on Van de Beek et al. (2012). This represents summer rainfall in the Netherlands, often being convective and hence to some extent assumed to be representative for Sri Lankan rainfall. Overeem et al. (2016) give a detailed description of the employed rainfall retrieval algorithm, the interpolation methodology and the implementation thereof in the RAINLINK software package, written in scripting language R. Data availability of CML rainfall maps is 100%. Note that rainfall maps cover entire Sri Lanka and surroundings, but that given the generally high spatial rainfall variability only grid cells should be used which are close to a CML antenna. To facilitate this, a column was added to the interpolation grid file "CMLInterpolationGridSriLanka.dat". By only selecting rows with a value of 1 in the last column, the grid cells are selected for which the nearest CML antenna is within approximately 5 km. More precisely stated: the distance to the nearest CML antenna was computed for each grid cell, where a CML had at least one path-averaged rainfall value during the 3.5-month period. This implies that for individual time intervals the distance to the nearest CML antenna may be (much) larger. Given the high availability of CML path-averaged rainfall, ranging from 22.6% to 100%, with a median value of 93.5% and an average value of 83.1%, the nearest CML antenna will indeed be within 5 km for most grid cells (with a value of 1 in the last column) and time intervals. The selected grid cells cover the majority of Sri Lanka, but are somewhat irregularly distributed over Sri Lanka. The reason for this is that not all CML data were available, CML data were discarded due to quality control and some areas have low CML network density.


# References

Overeem, A., Leijnse, H., and Uijlenhoet, R.: Retrieval algorithm for rainfall mapping from microwave links in a cellular communication network, Atmos. Meas. Tech., 9, 2425–2444, https://doi.org/10.5194/amt-9-2425-2016, 2016. 

Van  de  Beek, C.Z., Leijnse, H., Torfs, P.J.J.F., Uijlenhoet, R., 2012. Seasonal semi-variance of Dutch rainfall at hourly to daily scales, Adv. Water. Resour., 45:76–85,1542012. doi:10.1016/j.advwatres.2012.03.023.


# Data files:
- "CMLRainMapsSriLanka15min.zip": unpacking results in folder "CMLRainMapsSriLanka15min", which contains 15-min rainfall maps for 10624 time intervals, with one file for each interval. Each row contains the rainfall intensity (mm/h) for one grid cell. The file name contains the date and end time of observation (YYYYMMDDhhmm, i.e. year (2019), month (09), day (25), hour (08), minutes (00): 201109110800). Time zone is UTC+5:30, Indian Standard Time, which is the local time in Sri Lanka.
- "CMLInterpolationGridSriLanka.dat": the corresponding grid of the rainfall map files, with for each row the corresponding longitude, latitude, column number, row number, and index indicating whether nearest CML is within 5 km.
  

# Explanation of data fields:

RainIntensity 
Mean 15-min rainfall intensity in mm/h.

Longitude[degrees]
Longitude of middle of grid cell (degrees); WGS84.

Latitude[degrees]
Latitude of middle of grid cell (degrees); WGS84.

ColumnNumber
Column number, which can be efficient to use for visualization.

RowNumber
Row number, which can be efficient to use for visualization.

CMLAntennaWithin5km[0=no;1=yes]
Index indicating whether nearest CML is within approximately 5 km. 0: at least 5 km from nearest CML antenna; 1: within 5 km from nearest CML antenna.

