Since you are plotting the “Doppler Frequency” vs “azimuth” on figure it cannot be directly imported as an Image Format file in MATLAB. So, you may try to save the data in an Image format or can apply appropriate filtering for white noise on “Doppler Frequency” before plotting it onto figure.
For Both Image and “Doppler Frequency” vector you may use imgaussfilt which is effective at removing white noise from image. Also I can see different coloring in the figure So, I can assume there are some intensities attached with “Doppler Frequency”. I would suggests you to save the data in Image format and then apply imgaussfilt with sigma as your thresholding parameter. You may see the ‘FilterDomain’ parameter in imgaussfilt for getting appropriate filtering.