In this paper, we propose a novel Augmented Data Transmission (ADT) system which can transmit an additional data stream in the Advanced Television Systems Committee (ATSC) terrestrial DTV system. The proposed ADT system can offer an additional data of rate up to a few megabits per second (Mbps) based on hierarchical modulation, DTV signal cancellation, and advanced error correction code. The proposed ADT system significantly enhances capability compared with the data transmission schemes used in the transmitter identification (TxID) system. Since the proposed ADT system uses the in-band hierarchical modulation, it does not require any additional RF spectrum to increase the data capacity in a 6 MHz RF channel. Meanwhile, the ADT system has negligible impact to legacy receivers, if the proposed ADT system is deployed over the frequency bands occupied by ATSC A/53 or A/153 services.