Self-calibration and laser energy monitor validations for a double-pulsed 2-μm CO integrated path differential absorption lidar application.

Double-pulsed 2-μm integrated path differential absorption (IPDA) lidar is well suited for atmospheric CO remote sensing. The IPDA lidar technique relies on wavelength differentiation between strong and weak absorbing features of the gas normalized to the transmitted energy. In the double-pulse case, each shot of the transmitter produces two successive laser pulses separated by a short interval. Calibration of the transmitted pulse energies is required for accurate CO measurement. Design and calibration of a 2-μm double-pulse laser energy monitor is presented. The design is based on an InGaAs pin quantum detector. A high-speed photoelectromagnetic quantum detector was used for laser-pulse profile verification. Both quantum detectors were calibrated using a reference pyroelectric thermal detector. Calibration included comparing the three detection technologies in the single-pulsed mode, then comparing the quantum detectors in the double-pulsed mode. In addition, a self-calibration feature of the 2-μm IPDA lidar is presented. This feature allows one to monitor the transmitted laser energy, through residual scattering, with a single detection channel. This reduces the CO measurement uncertainty. IPDA lidar ground validation for CO measurement is presented for both calibrated energy monitor and self-calibration options. The calibrated energy monitor resulted in a lower CO measurement bias, while self-calibration resulted in a better CO temporal profiling when compared to the in situ sensor.