; (2) installation of additional physical barriers; (3) construction and maintenance of access and patrol roads; (4) lighting; (5) an interlocking surveillance camera system; (6) remote sensors; and (7) the purchase from the Secretary of Defense of surplus aircraft and unmanned aircraft systems. 4. Annual report on border security Not less frequently than once each fiscal year, the Secretary shall submit annually to the Committee on Homeland Security and Governmental Affairs of the Senate and the Committee on Homeland Security of the House of Representatives a report that describes for the applicable fiscal year— (1) the status of the construction of fencing and security improvements at United States borders; and (2) the estimated number of unlawful border crossings.