EKF: Fix bug in calculation of terrain observation variance

EKF/terrain_estimator.cpp

@@ -99,7 +99,7 @@ void Ekf::fuseHagl()
 		_hagl_innov = pred_hagl - meas_hagl;
 
 		// calculate the observation variance adding the variance of the vehicles own height uncertainty and factoring in the effect of tilt on measurement error
-		float obs_variance = fmaxf(P[8][8], 0.0f) + sq(_params.range_noise / _R_to_earth(2, 2));
+		float obs_variance = fmaxf(P[9][9], 0.0f) + sq(_params.range_noise / _R_to_earth(2, 2));
 
 		// calculate the innovation variance - limiting it to prevent a badly conditioned fusion
 		_hagl_innov_var = fmaxf(_terrain_var + obs_variance, obs_variance);