diff --git a/pyModeS/decoder/adsb.py b/pyModeS/decoder/adsb.py
index d3699ba..521ce1d 100644
--- a/pyModeS/decoder/adsb.py
+++ b/pyModeS/decoder/adsb.py
@@ -151,9 +151,16 @@ def velocity(msg):
         msg (string): 28 bytes hexadecimal message string
 
     Returns:
-        (int, float, int, string): speed (kt), ground track or heading (degree),
-            rate of climb/descend (ft/min), and speed type
-            ('GS' for ground speed, 'AS' for airspeed)
+        (int, float, int, string, string, string): speed (kt),
+            ground track or heading (degree),
+            rate of climb/descent (ft/min), speed type
+            ('GS' for ground speed, 'AS' for airspeed),
+            direction source ('gnd_trk' for ground track, 'mag_hdg' for
+            magnetic heading), rate of climb/descent source ('Baro' for
+            barometer, 'GNSS' for GNSS constellation).
+            
+            In the case of surface messages, None will be put in place
+            for direction, vertical rate, and their respective sources.
     """
 
     if 5 <= typecode(msg) <= 8:
diff --git a/pyModeS/decoder/bds/bds06.py b/pyModeS/decoder/bds/bds06.py
index bceb643..03ce272 100644
--- a/pyModeS/decoder/bds/bds06.py
+++ b/pyModeS/decoder/bds/bds06.py
@@ -147,9 +147,10 @@ def surface_velocity(msg):
         msg (string): 28 bytes hexadecimal message string
 
     Returns:
-        (int, float, int, string): speed (kt), ground track (degree),
-            rate of climb/descend (ft/min), and speed type
-            ('GS' for ground speed, 'AS' for airspeed)
+        (int, float, None, string, None, None): speed (kt),
+            ground track (degree), None for rate of climb/descend (ft/min),
+            and speed type ('GS' for ground speed), direction source
+            ('gnd_trk' for ground track), None rate of climb/descent source.
     """
 
     if common.typecode(msg) < 5 or common.typecode(msg) > 8:
@@ -182,4 +183,4 @@ def surface_velocity(msg):
         spd = kts[i-1] + (mov-movs[i-1]) * step
         spd = round(spd, 2)
 
-    return spd, trk, 0, 'GS'
+    return spd, trk, None, 'GS', None, None