Environmental tracking and formation control for a platoon of autonomous vehicles is studied. Vehicles travel through an environment that possesses a measurable scalar field, with the goal of moving in a desired spatial pattern about a desired constant value contour in the field. Each vehicle measures the local value of the field along its trajectory and shares information about its measurements and trajectory with other vehicles in the platoon. Platoon control involves estimation of a virtual leader trajectory coinciding with the target contour and about which vehicles form. Two approaches to leader estimation are considered. The first involves the synthesis of a common leader trajectory, whereas the second involves decentralized estimation of the leader trajectory by individual vehicles. Under the second approach, platoon control is posed as a two-level consensus problem, where vehicles reach agreement on the leader trajectory at one level and reach formation about the leader at the other level. The decentralized approach is effective even when communication among vehicles is limited. A target application involving an underwater vehicle platoon is considered.