More Signal Intensity Dependency Tests at Yarragadee

1. More Signal Intensity Dependency Tests at Yarragadee Randall Carman EOS Space Systems / Moblas5 ILRSTechnical Workshop - Eastbourne 2005

2. Introduction • We have conducted experiments to try & determine the magnitude of ranging biases induced by receive energy variation in a multi-photon SLR system. • In particular we want to try and find any biases induced by satellite signature (Centre of Mass) effects. ILRSTechnical Workshop - Eastbourne 2005

3. Acquiring Data • We use the receive path ND wheel to ensure Receive Energy continually varies throughout entire pass. This should eliminate elevation/predict induced biases. • Receive Intensity was maintained within normal system Dynamic Range. • In our previous attempt at high/low energy experiments (see Carman et al,2004), we didn’t allow for discriminator walk in our analysis. • To remedy this, an extended Calibration set was recorded for each pass, ensuring we had good data for the whole dynamic range of the pass. We then use this to generate a walk function. • Satellites targeted: Lageos 1&2, Ajisai, GFO-1, Stella, Starlette, Jason & Envisat. • Good Lageos 1&2 candidate passes rare. Sky conditions had to be perfect to get enough variation between weak and strong returns. ILRSTechnical Workshop - Eastbourne 2005

4. Pass Receive Energy Receive energies are varied throughout pass to avoid biases which may be induced by elevation changes or predicts. ILRSTechnical Workshop - Eastbourne 2005

5. Process - Analysis • Pass processed using regular np processor. • Extract and plot calibration receive energy and residuals for each data point. • Produce discriminator walk function from calibration data. • Extract and plot satellite residuals Vs Receive energy for each data point. • Edit outliers. • Remove discriminator walk from satellite data by applying previously calculated walk function. ILRSTechnical Workshop - Eastbourne 2005

6. Typical Calibration Curve Typical Receive energy Vs Single Shot Residual curve for an extended calibration set. Resulting 4th order polynomial trend function is applied to satellite residuals ILRSTechnical Workshop - Eastbourne 2005

7. CFD Walk Functions Polynomial functions calculated from extended calibration sets. ILRSTechnical Workshop - Eastbourne 2005

8. Results

9. Stella Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

10. Starlette Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

11. Lageos-1 Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

12. Lageos-2 Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

13. GFO-1 Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

14. Jason Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

15. Envisat Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

16. Ajisai Single Shot residuals Vs Receive Energy without Discriminator walk removed With Discriminator walk removed ILRSTechnical Workshop - Eastbourne 2005

17. Discussion • Although we will continue to take more experimental passes - it appears as though any biases induced by satellite signature are indeed small especially for the spherical satellites. • Some Satellite signature effect seems apparent for at least Ajisai. • How many photons are in the lowest level returns (35 mVnS) ? Some people suggest at least 3. How many in the high level? • We are seeing variations with time of the floor level of receive energies. The Integrator is probably inducing this +/-30 mVnS error. Maybe if we can eliminate this, we could see some finer effects. • The results do show how important it is to maintain as constant a receive energy throughout passes as possible to reduce biasing by Discriminator Walk. • At Yarragadee we should align the discriminators better for the the low return energies and restrict return energies above 800 mVnS during passes. ILRSTechnical Workshop - Eastbourne 2005

18. References • Carman,Noyes & Otsubo: Centre of Mass Correction Issues: Determining Intensity Dependency at a Multi-photon (Moblas5) station. Proc. International Workshop on Laser Ranging, San Fernando,2004. • Otsubo & Appleby: Centre of Mass Correction Issues: Towards mm Ranging. Proc. International Workshop on Laser Ranging, San Fernando,2004. ILRSTechnical Workshop - Eastbourne 2005