Testing Doppler Accuracy
 

Hi guys,
I was looking for a recommended method for testing of accuracy of Doppler accuracy over land and sea. I had some doubts regarding testing it using the triangular method of navigation wherein the installation errors will get concealed and may not give the operator accuracy of Doppler especially if there is a hybrid system on board. Also I would like to know if there is MIL standard recommending method of Doppler testing.

It's been many years since I last got involved with Doppler/TANS but I would suggest that Differential GPS (or even GPS) would give you the accuracies required at least for grid determination if not short term Drift & Hovermeter measurements. A good Inertial Reference System (IRS) should be able to give the lateral & longitudinal accelerations for that.

Any good?

Test and Evaluation of Aircraft Avionics and Weapons Systems by Robert E. McShea : Eurospan Bookstore

Test and Evaluation of Aircraft Avionics and Weapons Systems
Author(s): Robert E. McShea
List Price: £132.95

Anyone who wants some very old notes (+22yrs) on Doppler Nav systems testing, based on a couple of years of doing it at Boscombe Down, please pm me with your 'normal' email address.

You definitely need a good source of navigational truth data, particularly if you are trying to identify small installation or system errors. For gross navigation accuracy a cross-check with data from a WAAS enabled GPS receiver would be sufficient, particularly if you had a means of logging the doppler and GPS position and along-track velocity data for post-flight comparison. However, for a detailed system performance analysis you would definitely need an INS, or at the very least an IRS, with a real-time display of velocities and/or a data logger, to provide aircraft ground speed data (longitudinal and lateral) for comparison with the doppler system along-heading and cross-heading velocity outputs.

If you are limited to using GPS as your truth data, accurately flying several long, straight route segments would be useful, particularly if you fly it in both directions on a calm day to eliminate any wind-induced errors. If there is a systematic doppler error, you will know because on reaching the end of the segment there will be a position error. The cross-track position error should help you identify if the doppler antenna is not quite aligned with the aircraft longitudinal axis. Any significant systematic along-track error would indicate a problem with the doppler installation as a whole.

For position accuracy it is probably not worth the expense and hassle of using a DGPS system other than WAAS for your navigation truth data, simply because doppler accuracy is not good enough to justify the accuracy of the truth data. However, it may be worth investigating DGPS for as truth data for velocity accuracy, particularly for precision low-velocity doppler applications such as a hover meter. Otherwise an INS would be a good, albeit expensive, source of accurate velocity data.

Hope this helps!

WF

Doppler testing
 

Dear Sir,
Thank you for your offer- I would sincerely appreciate your interest in my query. My e-mail Id is [email protected].
Thanks a ton again.