Noise Performance of the Ganymed Laser Altimeter Receiver

We report here on qualification and calibration test results demonstrating the science performance of the Avalanche Photodiode (APD) detector of the Ganymede Laser Altimeter (GALA, Fig. 1). Most importantly, the measures for noise reduction of the analogue receiver electronics are described. This includes proper grounding of the APD module (EXCELITAS C30654) and filtering in its vicinity and the additional measures to isolate switching noise of the analogue-to-digital convertors (ADCs) from the sensitive single-ended analogue sensor pre-amplifier electronics of the APD. Tests with realistic electron irradiation doses being representative for the environment of the Jovian magnetosphere and additional shielding measures have been performed in order to ensure that the dark-current noise level of the receiver does not increase significantly over the mission time.