# Presentation: 860020

## Geosat Follow-On

- An examination from an ***operational*** point of view
- Impact on operational products
***Overall system*** performance (from sensor to product)
- At the present level, would the data be useful to operational products?
- What areas would lead to the most significant data improvement?

## System, from Sensor to Product

***System, from Sensor to Product***

- Altimeter Instrument	George Hayne, Dave Hancock	(GSFC)
- Water Vapor Radiometer	Chris Ruf	(Univ. Mich.)
- Satellite Timing Influence	John Lillibridge, Robert Cheney	(NOAA)
- Ionosphere Correction	Toni Mannucci	(JPL)
- Dry Troposphere	NOGAPS
- Satellite Orbit Position	Steve Klosko, Frank Lemoine	(GSFC)
- Cross-Comparisons	C.K. Shum	(Ohio St. Univ.)
- NAVO Processing	Gregg Jacobs, Kirk Whitmer	(NRL)

## Are the Data Good Enough?

***Are the Data Good Enough?***

- This is a misleading question
- Data is never good enough
- QC and error reduction are the make-or-break component of environmental prediction systems
- We must always strive to improve system accuracy, reduce data errors, and improve data QC

- Range Measurement
- Satellite Range
- Height above Ellipsoid
- Sea Level
- Non-tidal Sea Level
- Ocean Surface Pressure
- Temperature and Salinity Structure

- Radar Path Delays
- Orbit Solutions
- Geoid / Mean Ocean Height
- Tide Model
- Inverse Barometer (Atmospheric Load)
- MODAS Synthetics

***We must consider the entire system***

## Are the Data of Sufficient Quality to Include in Operation Products?

***Are the Data of Sufficient Quality to Include in Operation Products?***

- Would operational products (MODAS, NLOM) benefit from this data as it is now?
***Yes***
**Points that must be examined to demonstrate this:**
- How does NAVO deal with errors inherent in the present GFO data?
- To what level are the errors reduced?
- How do we know products would benefit?
- What is the product improvement from this data?

## Doppler Orbit Solution Errors

*GFO SSH using doppler orbits*

- Doppler-based orbit errors are on the order of a 2 meters
- The oceanographic signal is lost

## Laser Orbit Solution Errors

- Medium precision laser orbits errors are on the order of 10 cm
- Some of the larger scale ocean circulation begins to become apparent as individual track errors average out

*GFO SSH using medium precision orbits*

## TOPEX Orbit Solution Errors

- TOPEX GPS orbits have errors of a few cm
- Large scale ocean circulation as well as eddy features are visible
- Some ground tracks are obvious outliers due to orbit errors

*TOPEX SSH using GPS orbits*

## Orbit Error Corrections

***Orbit Error Corrections***

- We want to minimize orbit errors
- A majority of orbit error is concentrated at long wavelengths
- Taking advantage of this, we estimate and remove the orbit error from all data streams

- 0

- 0

- 0

- 4

- 2

- 4

- May 1, 2000

- July 20, 2000

*Estimated Orbit Error Amplitude*

## Doppler Vs. Laser Orbits after Correction

***Doppler Vs. Laser Orbits after Correction***

- We correct ALL altimeter data sets for orbit errors
- The post-correction difference is usually less than 1 cm

*SSH based on **Laser Orbits** minus SSH based on **Doppler Orbits*

## Data Quality Control

***Data Quality Control***

- TOPEX

- GFO

- All altimeter data streams pass through a series of quality control filters to detect and remove anomalous data
- Data removed by QC procedures is flagged and tracked daily
- QC removes any tracks in which data is found to be anomalous compared to historical data (orange), or in which orbit errors are not correctable (red)

## What Portion of the Data are of Use?

- 		Global	60S to 60N
- GFO	65%	81%
- TOPEX	85%	95%

***What Portion of the Data are of Use?***

- TOPEX and GFO processed by the NAVO operational software, ALPS
- Data from May 1 through July 5

- This analysis does not include ALL possible data, but all GDR data from NAVO
- Events such as the loss of data from being out of ERO are not included

- Percent of data usable for each day during May and June

- Most data above 60 N is lost (ERS-2 QC analysis)

## What are the Causes of Data Loss?

***What are the Causes of Data Loss?***

- Doppler orbit splicing appears to be the major contributor to data loss
- The tracks removed by the QC algorithms from December 1999 indicate laser-based SSH minus doppler-based SSH to have discontinuities

## What is the Data Accuracy?

***What is the Data Accuracy?***

- SSH Anomaly difference at points where satellite ground tracks cross one another indicate measurement errors (though actual oceanographic variations will affect the difference)
- RMS crossover differences of a satellite with itself are a measure of consistency and noise within the individual measurement system, while crossover differences with other satellites are a measure of consistencies between measurement systems

- SSH difference

- RMS Crossover differences (cm) between 55S and 55N

## SSH Anomaly

***SSH Anomaly***

- Offline T/P and GFO output from ALPS

***GFO***

***TOPEX***

## SSH Anomaly

- Offline T/P and GFO output from ALPS

***GFO***

***TOPEX***

## SSH Anomaly

- Offline T/P and GFO output from MODAS 2-D (analysis for June 15, 2000)

***GFO***

***TOPEX***

***GFO + TOPEX***

## Suppose There is an SSH Error, What are the MODAS Temperature Errors?

- Assume a 5 cm sea surface height error, what are the errors induced in MODAS synthetics?

## Expected SSH Errors

***Expected SSH Errors***

- Offline T/P and GFO output from MODAS 2-D (analysis for June 15, 2000)

***GFO***

***TOPEX***

***GFO + TOPEX***

- Missing Data

- Between tracks

## Models

***Models***

- The NLOM system is presently assimilating TOPEX and ERS-2

***NLOM SSH***

***NAVO BOGUS positions based on MCSST***

## Model Assimilation Errors

***Model Assimilation Errors***

- Based on twin model experiments
- Errors are dependent on ground track coverage and quantity of data
- Increased data quantity improves model results

## GFO

- A substantial portion (81%) of GFO data is presently useful in operational products
- Operational products will benefit from this data
- Data improvement efforts would continue to increase the data return and accuracy

***GFO***