Recurrent Neural Network (RNN), Long short-term memory (LSTM) for
Aerosol Optical Depth (AOD) using NASA’s MERRA-2 Reanalysis
Abstract
Predication of temporal trends of aerosol optical depth (AOD) within the
numerical climate models with enabled chemistry module is very
challenging and computationally expensive. In this work, new predication
model is introduced based on artificial neural networks (ANN) in order
to estimate average AOD over Egypt. Long short-term memory (LSTM)
algorithm which is artificial recurrent neural network (RNN)
architecture, is selected to construct the predication model. Seven
input datasets for LSTM algorithm are from NASA’s Modern-Era
Retrospective analysis for Research and Applications, Version 2
(MERRA-2) reanalysis within period (1980-2017). The seven variables are
pressure (PR), temperature (T), wind speed (W), dust surface particulate
matter (PM2.5), surface (SO2) and (SO4) concentrations and (CO)
concentration. AOD is the output of the trained and validated model.
Effects of changing the number of both hidden layers and number of
neurons per layers were evaluated. The results of increasing the number
of neurons per one hidden layer revealed that increasing the number of
neurons leads to three main finding (a) leads to faster convergence of
loss function. (b) Produces more realistic AOD estimation (c) RMSE is
reduced by increasing number of neurons. It was also found that, the
model with one hidden layer and 50 neurons is the best model setup with
RMSE (0.06). However, our studies showed also that increasing the number
of hidden layers has no dominant effect on model RNN performance. The
proposed LSTM model showed a very high level of accuracy with percentage
99.94 %. Future work can include more variables that has direct effect
on AOD calculations. Both ensemble algorithms and different datasets can
have more positive impact on the current proposed model.