On the Sensitivity of a Ground-Based Tropospheric Lidar to Aitken Mode Particles in the Upper Troposphere
Metadatos
Mostrar el registro completo del ítemEditorial
MDPI
Materia
Elastic lidar Sensitivity Signal-to-noise ratio Monte Carlo simulation Amazon New particle formation
Fecha
2022-10-01Referencia bibliográfica
Silva, M.T... [et al.]. On the Sensitivity of a Ground-Based Tropospheric Lidar to Aitken Mode Particles in the Upper Troposphere. Remote Sens. 2022, 14, 4913. [https://doi.org/10.3390/rs14194913]
Patrocinador
Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 132402/2020-3 308682/2017-3Resumen
Airborne observations have shown high concentrations of ultrafine aerosols in the Amazon
upper troposphere (UT), which are key for replenishing the planetary boundary layer (PBL) with
cloud condensation nuclei that sustain the “green ocean” clouds. Given their climatic relevance, longterm
observations are needed, but aircraft measurements are only available in short-term campaigns.
Alternatively, continuous observations of the aerosol vertical structure could be performed by a
lidar (acronym for “light detection and ranging”) system in long-term campaigns. Here we assess
whether a ground-based tropospheric lidar system could detect these ultrafine UT aerosols. To this
aim, we simulated the lidar signal of a real instrument and then varied the instrument’s efficiency
and the UT-particle concentration to determine under which conditions the detection is possible.
Optical properties were computed with a Mie code based on the size distributions and numerical
concentration profiles measured by the aircraft, and on the refractive indexes inverted from AERONET
measurements. The aerosol optical depth (AOD) was retrieved by inverting the elastic lidar signal,
and a statistical test was applied to evaluate the detection of the UT-aerosol layer. Our results indicate
that, for the instrument we simulated, a 55-fold increase in the signal-to-noise ratio (SNR) is required
for a 100% detection rate. This could be achieved by simultaneously time averaging over 30 min and
spatially averaging to vertical bin lengths of 375 m, or by modifying the hardware. We repeated the
analysis for under- and overestimated aerosol lidar ratio (Laer), and found that possible systematic
errors did not affect the detection rate. Further studies are necessary to assess whether such longtime
averages are feasible in the Amazon region (given the very high cloud cover), and to design a
hardware upgrade. Although simulations and analyses here were based on a particular instrument
and for the presence of new organic particles in the Amazonian upper troposphere, our methodology
and results are general and applicable to other instruments and sites.