# Presentation: 085256

## Recommendations from “RT/NRT user requirements” 

- E-GVAP recommends IGS to support PPP strategy with high quality adequate products.
- The 'real-time' clocks will be interesting future product for using in GPS meteorology. NRT clocks for current needs.
- NRT GPS ZTD product for NWP
- Requirements for “Costal real-time GPS network” (next slide)
- For climate applications, no need for RT/NRT, but to produce the ZTD product with long-term stability, high quality, and reduced diurnal bias, to increase the temporal coverage, to co-locate with radiosonde stations, to increase the sfc met data.
- Desirable product additions: NRT TEC with short term prediction (Grid or spherical harmonic coefficients and user algorithm), Sub daily EOP, Reference frame with periodical term included
- Possible improvements: Clocks without discontinuities and to Supply satellite DCB in SP3

## NASA Decision Project: GPS-aided Real-Time Earthquake and Tsunami (GREAT) Alert System

**Existing GDGPS (JPL/NASA)**

**Add into GDGPS**

**Coastal Real-Time GPS Network**

_**Technical Requirements:**_
**Network design (~10 km spacing)**
**Signal frequency (1 Hz)**
**Data accuracy (< 1 cm) **
**R/T GPS obits and clocks (10 sec)**
**Data processing ( 2 min)**
**GPS-inversion seafloor displacement & tsunami energy estimation (2 min)**
_**Logistical Requirements:**_
**International collaboration**
**Systems integration**

## From Historical Tsunamis to GPS Requirements

## E-GVAP and IGS

**E-GVAP is very thankful for the services that IGS provides the geodetic community. They are vital to the NRT GPS ZTD product that we use in meteorology.**
**For weather forecasting the GPS ZTD data must be available fast, and of a quality which is both good and does not fluctuate strongly in time.**
**The timeliness issue is important and clearly influences ZTD data quality.**

## Conclusions/Recommendations

**  ****GPS derived ZTDs are used operationally in Europe**
** **** ****Due to steadily increasing number of operational GPS sites PPP strategy presents a promising outlook for future efficient GPS-meteorology. E-GVAP recommends IGS to support PPP strategy with high quality adequate products.**
** **** ****The 'real-time' clocks will be interesting future product for using in GPS meteorology. **
**  ****For current needs E-GVAP encourages IGS to deliver clock products in ‘near-real’ time (hourly) till the ‘real-time’ IGS clocks will be available as products with sufficient quality**

## Summary – quality of IGU prediction

- after decommission of satellite G29 (October, 2008) there is no more significant difference in the standard orbit prediction performance.
- different pattern of the prediction can be seen during the eclipsing periods. We have to distinguish between satellites of old **Block-IIA **(fastly degrading) and new **Block-IIR **(modestly degrading) types.
- there are still 14 [15] of** old-type **satellites **active (45%):** G01, G03, G04, G05, G06, G08, G09, G10, G24, G25, G26, G27, G30, [G32].
- accuracy codes are in most cases relevant for the prediction, but usually **underestimated for Block-IIA during eclipsing** periods and at **the start of the maintenance periods**.
- currently 1-9h prediction are at least necessary for NRT/RT usage
- shorter prediction will be appreciated especially due to old Block-IIA satellites, but mainly for the NRT/RT (global) PPP applications.
_**Relevant question to AC’s:**_ how simply they can provide the orbits upgraded every 3h (+2h delay ?) with the same quality as of today ?
- (Even higher update rate could be requested for the PPP solutions).

## Future Needs

***Recommendations on improving future IGS products***

**To continuously produce the ZTD product and  maintain its long-term stability and high quality **
**To reduce diurnal biases in the ZTD product**
**To improve and increase sfc-met data**
**To co-locate with radiosonde stations**
**To increase the spatial and temporal coverage**

**Notes:**
So far hopefully I have convinced you on the value of the 2-hourly GPS-derived PW data for climate studies. But we can always do even better by working together. 
Based on our experience with the IGS ZTD product, we would like to make the following recommendations on improving future IGS products. 
The LT stability of the data is essential for climate studies. I will show you one example to illustrate this point.
I have shown you that the GPS PW data are very important for WV diurnal cycle studies, so we need to make efforts to reduce .. and in Ps and Tm used for PW derivation. This is especially true because we are dealing with a PW diurnal cycle of less than 5% that corresponds to ~0.24% change in ZTD.
Surface meteorology data, especially surface pressure, are required for calculating the dry delay and removing atmospheric pressure loading. Currently there are ~90 IGS stations that provide surface meteorology data. However, surface meteorology data are often very noisy and can not be used without careful examination and quality control. Besides improving the quality of surface meteorology data, more stations with surface pressure and temperature measurements are also needed, especially with the availability of 5-min ZTD data, since only surface meteorology data can provide 5-min surface pressure data to calculate ZHD. Furthermore, co-located surface meteorology data can be very useful for climate process studies. 
I have shown you how valuable the GPS PW dataset is for monitoring the quality of radiosonde humidity data. However, we found that the small displacements of GPS and radiosonde stations in space can make the comparisons complicated because of large variability of humidity in both space and time. Radiosonde data can be used to derive the mapping function for GPS data processing.
Incomplete temporal coverage in the IGS ZTD data makes it difficult to calculate monthly, seasonal, or even annual mean values. From 10-year of GPS PW data, we only found 13 stations with a complete 10-year record for PW trend calculations. I would appreciate for any info on why we have so much data dropout in ZTD data. In addition, it is important to add more IGS stations and integrate other regional GPS networks into the IGS network to increase the spatial coverage. 

## Desirable Product Addition/Upgrade

- NRT TEC with short term prediction
- in form of grid or spherical harmonic coefficients with a good user algorithm recovering correction values at arbitrary points
- Sub daily EOP
- will improve single epoch or short session (seconds to hours) applications
- Reference frame with well known periodical term included

- Possible Improvements

- Clocks without discontinuities (done already?)
- Supply satellite DCB in SP3