Similarity between two time series with different sampling frequency, different amplitude, and different lengths but taken from the same source?
What you could do is

downsample both series to match sampling rate between them
crop the longest series to match the shorter one

Then, there is a variety of methods to estimate similarity between the two series. Some of those are:

cross correlation: this will be affected by the amplitude and will not be able to estimate lagged correlations, prone to noise.
coherence: normalised frequency based correlation (cross-spectrum), not prone to amplitude or noise.
wavelet coherence: similar to above but based on wavelet transformations instead of STFFT.
dynamic time warping: measuring similarity between two temporal sequences, which may vary in speed.