There is a need for miniature, low power, and remotely powered sensors that can measure moisture and reactive gas content in the environment. Examples of devices that already exist include dew-point sensors, moisture sensors, and oxygen sensors. This disclosure describes the use of high-frequency ultrasonic pulses to interrogate thin films on the imaging surface of a CMOS integrated GHz Ultrasonic imager substrate. In one embodiment the device uses a Peltier cooler and heater chip to detect the dew point by the act of moisture condensing on the surface. Integrated temperature measurement is enabled by using some of the pixels, isolated from the environment, to be reflectors that measure the phase change in the reflected signal due to the change in the speed of sound in the silicon substrate. In another embodiment a thin film is exposed to gases, changing its ultrasonic impedance, which can be used to extract the film thickness and its ultrasonic properties.