I don't think it is an acronym at all. It is just a fancy name they gave to the system (trying to say that the import / export business would be working under "RADAR" suveillance).
If there is any other explanation, I am unaware of it.
Checked again in the site of Secretaria da Receita Federal, and all I get is the following definition:
RADAR (Registro e Rastreamento da Atuação dos Intervenientes Aduaneiros) So, that must be it.