-// Value of earth radius from [8]
-#define SG_EQUATORIAL_RADIUS_FT 20925650. // ft
-#define SG_EQUATORIAL_RADIUS_M 6378138.12 // meter
-// Radius squared
-#define SG_EQ_RAD_SQUARE_FT 437882827922500. // ft
-#define SG_EQ_RAD_SQUARE_M 40680645877797.1344 // meter
+/** Value of earth radius from LaRCsim (ft) */
+#define SG_EQUATORIAL_RADIUS_FT 20925650.
+
+/** Value of earth radius from LaRCsim (meter) */
+#define SG_EQUATORIAL_RADIUS_M 6378138.12
+
+/** Radius squared (ft) */
+#define SG_EQ_RAD_SQUARE_FT 437882827922500.
+
+/** Radius squared (meter) */
+#define SG_EQ_RAD_SQUARE_M 40680645877797.1344
+
+
+// Physical Constants, SI
+
+/**mean gravity on earth */
+#define SG_g0_m_p_s2 9.80665 // m/s2
+
+/**standard pressure at SL */
+#define SG_p0_Pa 101325.0 // Pa
+
+/**standard density at SL */
+#define SG_rho0_kg_p_m3 1.225 // kg/m3
+
+/**standard temperature at SL */
+#define SG_T0_K 288.15 // K (=15degC)
+
+/**specific gas constant of air*/
+#define SG_R_m2_p_s2_p_K 287.05 // m2/s2/K
+
+/**specific heat constant at constant pressure*/
+#define SG_cp_m2_p_s2_p_K 1004.68 // m2/s2/K
+
+/**ratio of specific heats of air*/
+#define SG_gamma 1.4 // =cp/cv (cp = 1004.68 m2/s2 K , cv = 717.63 m2/s2 K)
+
+/**constant beta used to calculate dynamic viscosity */
+#define SG_beta_kg_p_sm_sqrK 1.458e-06 // kg/s/m/SQRT(K)
+
+/** Sutherland constant */
+#define SG_S_K 110.4 // K
+