# Presentation: 167387

## Review

**Ionospheric Calibration for the GFO Altimeter**
- Xiaoqing Pi
- Byron A. Iijima
- Anthony J. Mannucci
- Mark J. Reyes
*Jet Propulsion Laboratory, California Institute of Technology*
- July 20, 2000.

## Outline

- Objectives:	Ocean altimeter calibrations
- Technology:	Remotely sensing the Earth’s ionosphere
- 			using GPS
- Resources:	GPS satellites and the IGS global GPS
- 			network
- Methodology:	Global ionospheric mapping (GIM)
- Ionospheric calibration for the GFO mission:
- An automated GIM processor for GFO altimeter calibrations
- Daily deliveries of calibration data
- Accuracy assessment
- Further development

## TEC Data Sources: The IGS Global GPS Network

- More than 300 permanent ground GPS stations are tracking 24~27 GPS satellites around the globe (the map shows selected sites) .
- Dual-frequency (L-band) GPS observables are recorded every 30-seconds.
- GPS data are collected in near real-time (NRT, hourly) or daily through Internet and phone lines, and archived at multiple centers.

## Global Ionospheric TEC Map

- Global snapshot of ionospheric TEC with a sub-hourly resolution
- Driven by GPS data collected from the global network

## Automated GIM Processor for Altimeter Calibrations

## GFO Deliveries

**Schedules**
- Daily delivery during May - August, 1999.
- Daily deliveries since the middle of February, 2000.
**Destinations**
- The Naval Oceanographic Office
- NOAA
**Products**
- Vertical TEC obtained from the GIM process along the satellite tracks.
- The TEC error estimate based on the statistics of TEC difference between GIM and TOPEX data.
- A backup (to be delivered if the GIM process fails): Vertical TEC obtained from the IRI95 empirical model.

## Validation

**Error Sources**
- Coarse coverage above oceans
- Slant-to-vertical mapping
- Data noise
- Ionospheric irregularities and scintillation
- Receiver malfunctioning
**Challenge**
- Geomagnetic and ionospheric storms** **
**Accuracy Assessment**
- Comparisons between GIM and independent ionospheric measurements (such as the TOPEX TEC) as well as empirical models
- Statistical analysis to assess the accuracy of GIM over the oceans

## TEC Comparisons between TOPEX and GIM/Models

- Date:  01/21/2000

## TEC Comparisons between TOPEX and GIM/Models

## TEC Comparisons between TOPEX and GIM/Models

## One-Day Histogram of Difference between Models and TOPEX

- For 13.5 GHz signals (GFO):    1 cm = 4.5 TECU    (1 TECU = 0.222 cm)

## Daily Mean Difference between Models and TOPEX

## Daily RMS of Difference between Models and TOPEX

## Largest Daily Positive Difference between Models and TOPEX

## Largest Daily Negative Difference between Models and TOPEX

## Further Development

**Measurements above oceans**
- GPS receivers on ships?
- GPS ocean reflections
- Other types of measurements?
**Global Assimilative Ionospheric Model (GAIM)**
- Assimilate ionospheric data into physics-based models
- Take ionospheric dynamics into account
- Overcome data coverage problems

## Ionospheric Data Assimilation

**GPS - TEC**

**DMSP - UV, N****e****, N****n**

**Ionospheric Mappers**
**TEC, N****e****, E, U****n****, ...**

**Data Processor**

**Forward Model**

**Ionosonde**
**Ne, h****m****F****2****, (v, U****n****)**

**Optimization**

**Model Drivers**

**State**
**Prediction**

**Observations**

**Adjustment of State **
**and Drivers**

**Data Selection**