diff --git a/src/aws/osml/photogrammetry/sicd_sensor_model.py b/src/aws/osml/photogrammetry/sicd_sensor_model.py
index d3c6be0..912d441 100644
--- a/src/aws/osml/photogrammetry/sicd_sensor_model.py
+++ b/src/aws/osml/photogrammetry/sicd_sensor_model.py
@@ -742,7 +742,7 @@ def rrdot_to_ground(self, r_tgt_coa, r_dot_tgt_coa, arp_position, arp_velocity)
                 np.sin(self.scp_lle.latitude),
             ]
         )
-        gref = self.scp_ecf.coordinate + (self.hae - self.scp_ecf.z) * u_gpn
+        gref = self.scp_ecf.coordinate + (self.hae - self.scp_lle.z) * u_gpn
 
         cont = True
         n = 1