  We discuss inverse problems of determining the time-dependent source
coefficient for a general class of subelliptic heat equations. We show that a
single data at an observation point guarantees the existence of a (smooth)
solution pair for the inverse problem. Moreover, additional data at the
observation point implies an explicit formula for the time-dependent source
coefficient. We also explore an inverse problem with nonlocal additional data,
which seems a new approach even in the Laplacian case.
