air raid vs carpet bombing

air raid

noun
  • An attack on a surface target by aircraft. 

  • A passing-heavy offensive scheme based on a shotgun formation with four wide receivers and a single running back. 

carpet bombing

noun
  • Large area bombardment done in a progressive manner to inflict damage in every part of a selected area of land. 

How often have the words air raid and carpet bombing occurred in a corpus of books? (source: Google Ngram Viewer )