IDA4D (Bust et al., 2000; Bust et. al, 2004) is a procedure which combines model output with actual measurement data. The algorithm organizes the data into spatial maps of electron density via an objective analysis technique, based upon three dimensional variational (3DVAR) data assimilation (Daley and Barker, 2001; Daley, 1991). These spatial maps are projected forward in time through a simple electron density continuity equation model, combined with a Gauss-Markov Kalman filter where they are used to initialize the next analysis. IDA4D takes into account data, data error covariances, a background model and the background model error covariances.
IDA4D is able to ingest any available observation of electron density or electron content.
At high latitudes,AMIE 3-D drift velocities are used in the electron continuity equation forward model to transport the plasma from one analysis step to the next. This has the advantage of improving the initial estimation of the density at the next analysis step, as well as providing more realistic density estimates in regions not supported by a rich set of data.
IDA4D has been validated (Coker et al., 2001; Watermann et al., 2002) and applied to several scientific investigations (Bust et al., 2000; Bust and Crowley, 2007; Yin et al., 2006; Garner et al., 2006; Crowley et al., 2006) and is used extensively at ASTRA.
ASTRA routinely collaborates with others and provides outputs of IDA4D. For more information please
Ground Based Data Sources currently accepted by IDA4D include:
1. Ground Based GPS TEC measurements
2. Ground Based “Beacon LEO” TEC measurements
3. DORIS TEC measurements
4. Digisonde time-delay versus frequency measurements (non-linear data source)
5. ISR measurements of electron density
1. In-situ measurements of electron density from satellites such as DMSP and CHAMP
2. GPS occultation TEC from CHAMP, COSMIC, SACC and GRACE.
3. GPS oversatellite TEC (OSEC) from CHAMP, COSMIC, SACC and GRACE
4. 1356 ÅUV radiances from GUVI and TIP (on COSMIC; non-linear data source)
5. CITRIS LEO satellite to LEO satellite TEC and occultations.