February 27, 2011

The Jason Microwave Radiometer (JMR) Enhanced Product provides an improved rain and sea ice flag valid for the radiometer data products and applies a recently developed coastal processing algorithm to provide wet tropospheric Path Delays (PD) near land, where the data were previously flagged as bad in the Geophysical Data Record (GDR).  The use of satellite altimetry for coastal studies has steadily increased over the past several years, but some of the science processing algorithms used to produce the data products on the GDR are either tuned for the open ocean or only valid in the open ocean and not valid in the coastal zone.  One such correction that is flagged as invalid in the coastal region is the radiometer derived wet tropospheric path delay correction.  Recent work by the Ocean Surface Topography Science Team (OSTST) and others has investigated this issue (Desportes et al. 2007; Mercier et al., 2008; Fernandes et al., 2010) and recently a new algorithm was developed to retrieve wet path delay in the coastal zone from the radiometer data and was first applied to the Advanced Microwave Radiometer (AMR) on Jason-2 (Brown 2010).  This so called Mixed-Pixel (MP) algorithm has been now applied to the Jason-1 radiometer and the data are available on the JMR Enhanced Product.

Algorithm Performance:

The performance of the algorithm is validated through detailed simulations and comparisons with the ECMWF model fields and ground based GPS derived path delays.  For the new JMR coastal product, the path delay errors are found to be unbiased relative to the near-by uncontaminated open ocean measurements and the RMS error is found to be less than 1.2 cm at 25 km from land and less than 1.5 cm at 10 km from land.  This represents a 2 cm reduction in error compared to the product available on the GDR.  The performance of the algorithm applied to the OSTM/Jason-2 Advance Microwave Radiometer (AMR) is even better because of the improved antenna design of the AMR compared to the JMR.  A comparison of the JMR and AMR path delays during the tandem mission in the coastal zone show they are unbiased with an RMS difference of less than 1cm, up to 10km from land.  An assessment of potential seasonal and regional biases revealed no significant geographically or temporally correlated systematic biases with the algorithm.

 

Data:

The time, latitude and longitude fields included in the enhanced product are identical to those on the Jason-1 GDR, and the number of records in each pass file is the same as on the GDR.  The enhanced wet troposphere path delay is identical to the rad_wet_tropo_corr field on the Jason-1 GDR greater than approximately 75 km from land.  Near the coast, an improved near land wet path delay algorithm is applied to improve the performance up to the coast.  The enhanced radiometer PD land flag that is included with the product is applicable to only the enhanced PD product.  The flag will be 2 (invalid) when the radiometer boresight is centered on the coastline and remain 2 when the radiometer is over land.  The flag will be 1 (valid) if the coastal processing has been applied and will be 0 (valid) if the open ocean processing has been applied.  The radiometer land flag on the GDR is valid only for the GDR PD and not the enhanced PD.  The sea ice flag indicates if the radiometer path delay measurement should be considered invalid due to sea ice contamination.  This flag is applicable to both the GDR PD and the new enhanced PD.  The sea ice flag is 0 if the measurement is valid and 1 if the measurement is invalid due to sea ice.  The rain ice flag indicates if the radiometer path delay measurement should be considered invalid due to rain contamination.  This flag is applicable to both the GDR PD and the new enhanced PD.  The rain flag is 0 if the measurement is valid and 1 if the measurement is invalid due to rain.
All questions/comments/feedback about the product should be directed to Shannon Brown (Shannon.T.Brown@jpl.nasa.gov).

References:

  • F. Mercier, G. Dibarboure, C. Dufau, L. Carrere, P. Thibaut, E. Obligis, S. Labroue, M. Ablain, P. Sicard, G. Garcia, T. Moreau, L. Commien, N. Picot, J. Lambin, E. Bronner, A. Lombard, A. Cazenave, J. Bouffard, M. C. Gennero, F. Seyler, P. Kosuth, and N. Bercher, “Improved Jason-2 altimetry products for coastal zones and continental waters (PISTACH Project),” presented at the EUMETSAT Meteorological Satellite Conf., Darmstadt, Germany, 2008.
  • C. Desportes, E. Obligis, and L. Eymard, “On the wet tropospheric correction for altimetry in coastal regions,” IEEE Trans. Geosci. Remote Sens., vol. 45, no. 7, pp. 2139–2149, Jul. 2007.
  • M. Joana Fernandes, Clara Lázaro, Alexandra L. Nunes, Nelson Pires, Luísa Bastos, and Virgílio B. Mendes, “GNSS-Derived Path Delay: An Approach to Compute the Wet Tropospheric Correction for Coastal Altimetry,”  ,” IEEE Geosci. Remote Sens. Letters, vol. 7, no. 3, pp. 596-600, Jul. 2010.
  • Brown, S., "A Novel Near-Land Radiometer Wet Path Delay Retrieval Algorithm:  Application to the Jason-2/OSTM Advanced Microwave Radiometer", IEEE Trans. Geosci. Remote Sens., vol. 48, no. 4, pp. 1986–1992, April, 2010.