A Solid State DIAL System for Water Vapor Profiling

We have created a conceptual design for a compact, automated DIfferential Absorption LIDAR (DIAL) for water vapor profiling to the tropopause. This DIAL sensor is intended to be the primary component of the Integrated Upper Atmosphere Water Vapor Sensor concept being developed by the National Weather Service (NWS). The DIAL sensor is a monostatic LIDAR design operating with a pulsed laser transmitter and direct detection of the returned energy. The laser transmitter is a Master Oscillator/Power Amplifier design using a near-IR diode laser as the master oscillator and an erbium-doped fiber amplifier as the power amplifier. The seed laser operates near 1.5 mm. The transmitter will produce 12 mJ/pulse at 8 kHz repetition rate and will qualify as a Class I device using a 5 inch diameter transmit optic. The receiver telescope diameter is 14 inches. Return power is detected via InGaAs based Avalanche PhotoDiodes used in photon counting mode. Both near and far field channels are used to handle the dynamic range of the return signal. The DIAL sensor will operate continuously and autonomously and have a vertical resolution of 200 m and a temporal resolution of 10 minutes throughout the troposphere. Water vapor retrievals are predicted to have a precision of ≤ 5% for altitudes ≤ 4.4 km, capturing 93% of total H₂O column on average. Retrievals are predicted to have a precision of ≤ 19% for altitudes ≤ 6 km capturing 98% of total H₂O column on average. Conceptual system and packaging designs have been developed. These designs envision a compact, environmentally conditioned sensor package that will operate autonomously.