diff --git a/libraries/SondeLib/nav_gps_vel.cpp b/libraries/SondeLib/nav_gps_vel.cpp
index da933b3..afd1ccc 100644
--- a/libraries/SondeLib/nav_gps_vel.cpp
+++ b/libraries/SondeLib/nav_gps_vel.cpp
@@ -1,6 +1,7 @@
-
-/*
-  Quellen:
+/* SPDX-License-Identifier:        GPL-3.0
+ * based on https://github.com/rs1729/RS/blob/master/rs92/nav_gps_vel.c
+ *
+ Quellen:
            - IS-GPS-200H  (bis C: ICD-GPS-200):
              http://www.gps.gov/technical/icwg/
            - Borre: http://kom.aau.dk/~borre
diff --git a/libraries/SondeLib/rs92gps.cpp b/libraries/SondeLib/rs92gps.cpp
index 019b029..f011172 100644
--- a/libraries/SondeLib/rs92gps.cpp
+++ b/libraries/SondeLib/rs92gps.cpp
@@ -1,5 +1,6 @@
-
-/*
+/*  SPDX-License-Identifier:        GPL-3.0
+ *  based on https://github.com/rs1729/RS/blob/master/rs92/rs92gps.c
+ * 
  *  radiosonde RS92
  *
  *