is also known. Light sampling counts are eliminated from the data since an "out" 1 is cancelled by an "in" -1, resulting in a cumulative count of zero for light sampling bats. Thermal imagers which are of a high enough definition to register bats at over 30 metres range are expensive, but have been used to assess the dangers of wind turbines to birds and bats. "Affordable" thermal imagers have a bat detecting range about the same order of acoustic bat detectors due to the small size and the low heat emissions of bats. Passive infrared sensors are slow with a response speed of the order of a tenth of a second and will normally not detect a small fast mammal like a bat. Radar has been used to detect bats beyond the acoustic limit, but is very costly in equipment and man hours. Bird Aircraft Strike Hazard (BASH) installations are capable of detecting bats, but are usually situated where few bats fly. There are very few suitable mobile terrestrial radars available anywhere. Hand-held doppler radar modules have been used in the field to allow researchers to compensate for the doppler shift imposed on recordings of bat signals due to their flight speed. This allows the researchers to tell whether the bats are changing the pitch of their calls in flight. See also Bat species identification References External links Bat Detector Reviews Build a Simple Bat Detector Guide to Bat Detectors from the Bat Conservation Trust New Jersey Society for Amateur Scientists: Building a Simple Bat Detector Bats and humans Detectors Sound technology Ultrasound