Providing your AM's and AP's are set to scan DFS channels and a radar event occurs, you should see something similiar to the below.
(WLC-001) #show ap arm history ap-name WAP01
Interface :wifi0
ARM History
-----------
Time of Change Old Channel New Channel Old Power New Power Reason
-------------- ----------- ----------- --------- --------- ------
2017-03-27 18:15:22 44+ 44+ 15 18 P+
2017-03-27 18:06:10 44+ 44+ 12 15 P+
2017-03-27 17:38:03 44+ 44+ 18 12 P-
2017-03-09 16:50:54 100+ 44+ 18 18 M
2017-03-09 04:45:53 124+ 100+ 18 18 I
2017-03-09 04:20:39 124+ 124+ 15 18 P+
2017-03-09 04:14:10 100+ 124+ 18 18 R
2017-03-09 02:17:44 100+ 100+ 15 18 P+
2017-03-09 02:12:29 108+ 100+ 18 18 R
2017-03-09 00:24:58 108+ 108+ 15 18 P+
2017-03-09 00:19:14 108+ 108+ 12 15 P+
2017-03-09 00:18:23 60+ 108+ 12 12 M
2017-03-09 00:01:36 60+ 60+ 9 12 P+
2017-03-08 23:59:32 124+ 60+ 9 9 M
2017-03-08 23:55:12 100+ 124+ 9 9 M
2017-03-08 23:54:54 100+ 100+ 15 9 P-
2017-03-08 23:39:17 108+ 100+ 18 18 R
2017-03-08 21:46:11 108+ 108+ 15 18 P+
2017-03-08 21:38:21 60+ 108+ 18 18 R
2017-03-08 21:34:09 60+ 60+ 15 18 P+
2017-03-08 21:32:43 100+ 60+ 15 15 M
2017-03-08 21:18:14 124+ 100+ 18 18 R
2017-03-08 21:05:18 124+ 124+ 15 18 P+
2017-03-08 21:04:55 116+ 124+ 15 15 M
2017-03-08 20:58:05 108+ 116+ 18 18 R
2017-03-08 20:17:53 108+ 108+ 15 18 P+
2017-03-08 20:17:44 100+ 108+ 18 18 R
2017-03-08 19:57:35 100+ 100+ 15 18 P+
2017-03-08 19:54:22 44+ 100+ 15 15 I
2017-03-08 19:49:29 60+ 44+ 15 15 M
2017-03-08 19:38:28 108+ 60+ 18 18 R
2017-03-08 17:52:44 108+ 108+ 15 18 P+
Interface :wifi1
I: Interference, R: Radar detection, N: Noise exceeded, Q: Bad Channel Quality E: Error threshold exceeded, INV: Invalid Channel, G: Rogue AP Containment, M: Empty Channel, P+: Increase Power, P-: Decrease Power, 40INT: 40MHZ intol detected on 2.4G, NO40INT: 40MHz intol cleared on 2.4G, OFF: Turn off Radio, ON: Turn on Radio
Are you able to confirm that any radar events are actually occuring? Depeding on hold old the AP's are, they may not support the feature.
https://community.arubanetworks.com/t5/Controller-Based-WLANs/What-is-Dynamic-Frequency-Selection-DFS-How-to-Enable-it-What/ta-p/179170
#show rf am-scan-profile default
AM Scanning profile "default"
-----------------------------
Parameter Value
--------- -----
Scan Mode all-reg-domain
Dwell time: Active channels 500
Dwell time: Regulatory Domain channels 250
Dwell time: non-Regulatory Domain channels 200
Dwell time: Rare channels 100
Do you have any more info about your configuration, AP type, regulatory domain and so on?
Thanks