Sensors mounted on vehicles (e.g., buses, taxis, police cars) and public personnel (e.g., policemen) are used to monitor various conditions and situations such as air quality, potential biological and chemical attacks, and road and traffic conditions. The invention improves upon the typical approach that deploys fixed sensors at every geographical position of interest. The total number of required sensors and the size and the complexity of the network infrastructure required to connect the sensors are reduced and simplified. A method for estimating the number of mobile sensors required to cover a region of interest also is disclosed. A relatively small number of mobile sensors may be sufficient to cover a large area at a lower cost and less complexity than a fixed sensor network.