Discussion om the use of radar sweeps vs 5min accumulated radar images for pysteps inputs

[sidekock]

I have had this discussion with quite a few people over the last few years, but so far, no clear answer has ever been formulated, let alone that it would lead to even clearer documentation.
The question is the following:
All the STEPS (blended) nowcasting modules expect a sequence of rain rates in mm/h which will then be converted in the code. However nowhere is it specified what the contents of these fields should be. In general there are two possible origins (lets assume the QPE uptate is done every 5min for simplicity):

1. Use the latest radar sweep reconstructed into a 2D QPE
2. Use the latest radar sweep and the one before, together with the last rain gauge information to get the last 5 minute accumulated QPE
   These can then both be converted into a rate-like-product (in mm/h) but that is just a bookkeeping issue. The real question is which field is physically more correct to advect forwards aswel as if that is the best field to advect forward from an engineering point of view. This might be worth discussing during the hackathon