text: Title: BUG: NEXRAD Level3 DPR  product reading
  Body: I am doing project on Quantitative Precipitation Estimation using WSR 88D Radar. I am comparing NEXRAD L3 Digital Precipitation Rate with actual Rain Rate from TRMM GV Rain Gauges.
  
  Looks like the data being read in the below snippet does not scale the rain rate data correctly.
  https://github.com/ARM-DOE/pyart/blob/a68bed26f6380eecbf1042c94bd4da0b60fb2da7/pyart/io/nexrad_level3.py#L297-L300
  
  The way I am seeing the data, I need to multiply the whole data by 10. To convert it to the proper scale (i.e. inch/mm).
  
  Below are some Z-RR plots at a constant height. Z is obtained from NEXRAD L2 data. Additionally I am also multiplying the Pyart read DPR data by 25.4 to convert it to mm/hr. But that is not expected by pyart as L3 DPR data is supposed to have default unit as inch/mm.
  
  L3 DPR data after reading it through pyart and converting to mm/hr.
  ![2015_rr_vs_z_0 5_gauge_SFL_068](https://user-images.githubusercontent.com/64808466/163691993-1111948c-4983-45cf-a0c7-e1b767ee7125.png)
  
  L3 DPR data after reading it through pyart, multiplying by 10 and converting to mm/hr.
  ![2015_rr_vs_z_0 5_gauge_SFL_068 (1)](https://user-images.githubusercontent.com/64808466/163692079-f8066ea3-af40-4758-8693-803d8622a632.png)
  
  I hope this explanation helped. This is not a significant issue but would still be good to avoid confusion while reading the DPR data.
  
  Btw, thanks for creating this wonderful tool for reading L3 data. There are not a lot of tools that do that. Found it very helpful. :)
  