  We present a field report of CTU-CRAS-NORLAB team from the Subterranean
Challenge (SubT) organised by the Defense Advanced Research Projects Agency
(DARPA). The contest seeks to advance technologies that would improve the
safety and efficiency of search-and-rescue operations in GPS-denied
environments. During the contest rounds, teams of mobile robots have to find
specific objects while operating in environments with limited radio
communication, e.g. mining tunnels, underground stations or natural caverns. We
present a heterogeneous exploration robotic system of the CTU-CRAS-NORLAB team,
which achieved the third rank at the SubT Tunnel and Urban Circuit rounds and
surpassed the performance of all other non-DARPA-funded teams. The field report
describes the team's hardware, sensors, algorithms and strategies, and
discusses the lessons learned by participating at the DARPA SubT contest.
