Principal component analysis (PCA) and nonlinear principal component analysis (NLPCA) are used to detect ionospheric anomalies. The ionospheric anomalies related to Haiti earthquake on 12 January 2010 are researched by PCA in Chapter 1. The ionospheric anomalies related to Taiwan Chi-Chi earthquake on 21 September 1999 are researched by NLPCA in Chapter 2. The ionospheric anomalies related to Japan Tohoku earthquake on 11 March 2011 are researched by PCA and image processing in Chapter 3.