10 dB 5 dB 100 50 50 100 Pulse Index 5 -5 100 -100 100 Pulse Index FIGURE 17. Sparsity-based autofocusing of ISAR imaging under three different types of phase error (low order, high order, and random) [81]. 40 80 120 40 80 120 40 80 120 100 Pulse Index 120 100 80 60 40 20 120 100 80 60 40 20 120 100 80 60 40 20 120 100 80 60 40 20 40 80 120 120 100 80 60 40 20 40 80 120 120 100 80 60 40 20 40 80 120 40 80 120 40 80 120 40 80 120 120 100 80 60 40 20 120 100 80 60 40 20 120 100 80 60 40 20 0 dB 10 dB 5 dB 160 120 80 100 160 120 80 100 160 120 80 100 Doppler Cell 200 200 160 120 80 100 Doppler Cell 200 200 160 120 80 100 200 160 120 80 100 Doppler Cell FIGURE 18. A comparison of ISAR autofocusing using the weighted-least-squares (WLS), minimum-entropy [170], and sparsity-based autofocusing [81]. 56 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE DECEMBER 2022 200 160 120 80 100 100 200 200 160 120 80 100 200 160 120 80 100 100 200 0 dB Sparsity-Driven Range Cell Minimum Entropy Range Cell WLS Phase Error 3 (rad) Range Cell Phase Error 2 (rad) Phase Error 1 (rad)