diff --git a/acoustic_msgs/msg/PingInfo.msg b/acoustic_msgs/msg/PingInfo.msg
index f2f8d7b..2eaeab5 100644
--- a/acoustic_msgs/msg/PingInfo.msg
+++ b/acoustic_msgs/msg/PingInfo.msg
@@ -1,11 +1,26 @@
+# the frame id of the acoustic center of the receiver
+# the transmitter frame is assumed to be that specified
+# in the message header
+string rx_frame_id
+
+# the ping number reported by the sonar.
+# useful for matching multiple message types for a given ping
+uint64 ping_no
+
 # Center frequency of sonar in Hz
 # Set to 0 if unavailable
 float32 frequency
 
+# the width of the transmittd pulse in seconds
+float32 tx_pulse_width
+
 # Speed of sound (m/s) used to calculate ranges;
 # Set to 0 if unavailable
 float32 sound_speed
 
+# The number of samples per second that the reciever collects
+float32 sample_rate
+
 # Sonar reported -3db beamwidths
 # May be empty if not reported
 # reported in radians
diff --git a/acoustic_msgs/msg/RawSonarImage.msg b/acoustic_msgs/msg/RawSonarImage.msg
index ef7c5a2..8432edf 100644
--- a/acoustic_msgs/msg/RawSonarImage.msg
+++ b/acoustic_msgs/msg/RawSonarImage.msg
@@ -1,14 +1,11 @@
-
-# The header time should be the time the ping was transmitted, not
-# the time the message was received.
-# Note that these two could potentially be several seconds apart,
-# especially in deep water.
+# All values in the header are associated the transmitter:
+# 	- stamp references the transmit time or the start of the
+#	  transmit cycle.
+#	- frame_id references the transmitter's acoustic center
 std_msgs/Header header
 
 PingInfo ping_info
 
-float32 sample_rate   # hz
-
 uint32  samples_per_beam  # the number of samples in each beam
 
 # Many sonars have some kind of upper gate for water column data
@@ -16,8 +13,14 @@ uint32  samples_per_beam  # the number of samples in each beam
 # for beam n
 uint32 sample0
 
+# if the image is not reported at the full resolution
+# ping_info.sample_rate != image_sample_rate
+# for a given sample:
+#   2-way travel time = image_sample_rate*(sample_no+sample0)
+
+float32 image_sample_rate
+
 # Multi-sector multibeams can transmit different sectors at different times
-# The Reson doesn't but we include a TX delay for each beam anyway.
 #
 # Overall, therefore, our overall time is:
 #
@@ -25,11 +28,12 @@ uint32 sample0
 # Each beam's TX time: header.stamp + transmit_delay[i]
 # Each beam's RX time: header.stamp + transmit_delay[i] + sample_rate*image_row
 float32[] tx_delays
-# Steering angle applied to tx beam
+
+# The angle reported for the transmitted pulse
 # reported in radians
 float32[] tx_angles
 
-# Steering angle applied to rx beam
+# The angle reported for the received pulse
 # reported in radians
 float32[] rx_angles
 
diff --git a/acoustic_msgs/msg/SonarImageData.msg b/acoustic_msgs/msg/SonarImageData.msg
index abb88c2..f1b724f 100644
--- a/acoustic_msgs/msg/SonarImageData.msg
+++ b/acoustic_msgs/msg/SonarImageData.msg
@@ -17,4 +17,6 @@ uint32  dtype
 uint32 beam_count
 
 # The actually pixel data in row-major (beam_index major) format
+# this can be interpreted as a 2d array with indicies beam_index and
+# sample_number
 uint8[] data