diff --git a/lib/xmet/rawins.py b/lib/xmet/rawins.py
index cfdc537..683e2ab 100644
--- a/lib/xmet/rawins.py
+++ b/lib/xmet/rawins.py
@@ -152,6 +152,15 @@ class RawinsObs():
             }
 
     def parse_ttaa(self):
+        #
+        # Return None if there is no height data up to 100mb.
+        #
+        if self.values[0][4] != '1':
+            return None
+
+        #
+        # Return None if there is no station identifier.
+        #
         if self.values[1][0:3] == 'NIL':
             return None