Analysis Centre Software - POD

Overview

The Analysis Centre Software (ACS) is a processing package being developed to processes GNSS observations for geodetic applications.

We currently support the processing of:

• the American Global Positioning System (GPS); and
• the Chinese Navigation Satellite System (Beidou)

We are actively developing the ACS to have the following capabilities and features:

• Precise Orbit & Clock determination of GNSS satellites (GNSS POD).
• Precise Point Positioning (PPP) of GNSS stations in network and individual mode.
• Real-Time corrections for PPP users.
• Analyse full, single and multi-frequency, multi-GNSS data.
• Delivering atmospheric products such as ionosphere and troposphere models.
• Servicing a wide range of users and receiver types.
• Delivering outputs usable and accessible by non-experts.
• Providing both a real-time and off-line processing capability.
• Delivering both position and integrity information.
• Routinely produce IGS final, rapid, ultra-rapid and real-time (RT) products.

The software is broken into two main components:

• the Network Parameter Estimation Algorithm (PEA-N); and
• the Precise Orbit Determination (POD).

POD

The ACS Version 0.0.1 beta release supports:

1. The POD

Directory Structure

pod/
├── README.md

Dependencies

1. The lapack numerical linear algebra library (lapack.x86_64) (You may need to run the command ln -s /usr/lib64/liblapack.so.3 /usr/lib64/liblapack.so)
2. The basic linear algebra library (blas.x86_64,liblas-libs.x86_64) (You may need to run the command ln -s /usr/lib64/libblas.so.3 /usr/lib64/libblas.so)

Build

To build the POD ...

$ cd pod
$ make

You should now have the executable 'main_orb.e'

Configuration File

The POD Precise Orbit Determination (./main_orb.e) uses the configuration file: ├── EQM.in (Full force model equation of motion) ├── VEQ.in (For variational equations)

Processing Example #1

In this example the pod will perform a dynamic orbit determination for PRN04 over a 6 hour arc. The full gravitational force models are applied, with a cannonball model SRP model.

To run the POD ...

$ ./main_orb.e

This should output the following to stdout...

Orbit Determination
Orbit residuals in ICRF : RMS(XYZ)   1.6754034501980351E-002   5.2908718335411935E-002   1.5676115599034774E-002
Orbit Determination: Completed
CPU Time (sec)   298.48134399999998
External Orbit comparison
Orbit comparison: ICRF
RMS RTN   2.8094479714173427E-002   2.4358145601708528E-002   4.4097979280889953E-002
RMS XYZ   1.6754034501980351E-002   5.2908718335411935E-002   1.5676115599034774E-002
Orbit comparison: ITRF
RMS XYZ   3.9069978513805753E-002   3.9343671258381237E-002   1.5660654272651970E-002
Write orbit matrices to output files
CPU Time (sec)   349.19307899999995

The results above show that our orbits arcs, over 6 hours, are currently within 2-5 cm of the final combined IGS orbit.

The prcessing also produces the following output files...

├── DE.430            planetary ephemris intermediate file
├── Amatrix.out       design matrix
├── Wmatrix.out       reduced observation matrix
├── orbext_ICRF.out   intermediary file for the IGS orbit solution in ICRF for comparison purposes
├── orbext_ITRF.out   intermediary file for the IGS orbit solution in ITRFfor comparison purposes
├── dorb_icrf.out     differences in solutions in ICRF
├── dorb_RTN.out      differences in solutions in orbital frame components radial, tangential and normal (RTN)
├── dorb_Kepler.out   differences in solutions in keperian elements 
├── dorb_itrf.out     differences in solutions in ITRF 
├── orb_icrf.out      the final estimated orbit in ICRF
├── orb_itrf.out      the final estimated orbit in ITRF
├── VEQ_Smatrix.out   State transition matrix from the variational equations solution
├── VEQ_Pmatrix.out   Sensitivity matrix from the variational equations solution

Processing Example #2 - ECOM2 SRP

In this example we will change the SRP model to use the ECOM2 model.

Edit the EQM.in file so that the Solar Radiation Pressure configuration section now looks:

! Solar Radiation Pressure model: ! 1. Cannonball model ! 2. Box-wing model ! 3. ECOM (D2B1) model SRP_model 3

Then edit VEQ.in, so that the Non-gravitational forces now looks like:

%% Non-gravitational Effects Solar_radiation 0 Earth_radiation 0 Antenna_thrust 0

! Solar Radiation Pressure model: ! 1. Cannonball model ! 2. Box-wing model ! 3. ECOM (D2B1) model SRP_model 3

run the POD ...

$ ./main_orb.e

This should output the following to stdout...

Orbit Determination
Orbit residuals in ICRF : RMS(XYZ)   2.0336204859568077E-002   8.4715644601919167E-003   3.9687932322714677E-002
Orbit Determination: Completed
CPU Time (sec)   299.68054799999999
External Orbit comparison
Orbit comparison: ICRF
RMS RTN   2.8182836396022540E-002   2.4598832384842121E-002   2.5879201921952168E-002
RMS XYZ   2.0336204859568077E-002   8.4715644601919167E-003   3.9687932322714677E-002
Orbit comparison: ITRF
RMS XYZ   1.8757217704973204E-002   1.1635302426688266E-002   3.9702619816620370E-002
Write orbit matrices to output files
CPU Time (sec)   350.88653299999999