The classification of ignitable liquids,
such as gasoline, is critical
crime scene intelligence to assist arson investigations. Rapid field
gasoline classification is challenging because the current forensic
testing standard requires gas chromatography–mass spectrometry
analysis of evidence in an accredited laboratory. In this work, we
reported a new intelligent analytical platform for field identification
and classification of gasoline evidence. A hand-held Raman spectrometer
was utilized to collect Raman spectra of reference gasoline samples
with various octane numbers. The Raman spectrum pattern was converted
into image presentations by continuous wavelet transformation (CWT)
to facilitate artificial intelligence development using the transfer
learning technique. GoogLeNet, a pretrained convolutional neural network
(CNN), was adapted to train the classification model. Six different
classification models were also developed from the same data set using
conventional machine learning algorithms to evaluate the performance
of our new approach. The experimental results indicated that the pretrained
CNN model developed by our new data workflow outperformed other models
in several performance benchmarks, such as accuracy, precision, recall,
F1, Cohen’s Kappa, and Matthews correlation coefficient. When
the transfer learning model was challenged with the data collected
from weathered gasoline samples, the classifier could still offer
73 and 53% accuracy for 50 and 25% weathered gasoline samples, respectively.
In conclusion, wavelet transforms combined with transfer learning
successfully processed and classified complex Raman spectral data
without feature engineering. We envision that this nondestructive,
automated, and accurate platform will accelerate crime scene intelligence
development based on evidence’s chemical signatures detected
by hand-held Raman spectrometers.