# Presentation: 078553

## Aeolus Level-2B Wind RetrievalAlgorithms and SoftwareDavid Tan ECMWF 14th CLRCSnowmass Colorado 2007

- DLR: Oliver Reitebuch
- DoRIT: D. Huber
- ECMWF: D. Tan, E. Andersson, F. Hofstadler, I. Mallas
- KNMI: J. de Kloe, G.-J. Marseille, A. Stoffelen
- LMD: P. Flamant
- Meteo-France: P. Poli, M.-L. Denneulin, A. Dabas
- Plus: M. Rohn (DWD), Mission Advisory Group, ESA

## Talk Outline

**Introduction**
**What are the Level-2B/2C Wind Products?**
**How do they differ from Level-1B Products?**
**Strategy and implementation**
**Who will make them?**
**Why distribute source code for the L2BP?**
**Does it work?**
**Main algorithm components**
**Retrieval examples, future work**
**How will L2BP source code be distributed?**

## 1a/b. What are Level-2B/2C Products?

## 1a/b. What are Level-2B/2C Products?

**2B: Meteorologically representative ****HLOS**** profiles**
**retrieval algs applied to Level-1B data, 2B-output suitable as input to data assimilation**
- auxiliary input data: T & p, Rayleigh-Brillouin response data, etc
**2C: Meteorologically representative ****wind vector**** profiles**
**result of a data assimilation algorithm, combining Level-2B with other data/weather forecast model**
**How do they differ from Level-1B Products?**
**Rayleigh channel retrieval accounts for T & p effects**
**measurements grouped/weighted by features detected in the atmospheric scene (primarily clouds & aerosol)**

## 2a.  Who will make Level-2B/2C Products?

**ECMWF for “operational” Level-2B/2C products**
**Processing integrated with data assimilation system**
**Products in ESA’s Earth Explorer file format available from ESA (Long-Term Archive)**
**ESA LTA for Level-2B late- & re-processing**
**Level-1B missing ECMWF’s operational schedule**
**New processing parameters/auxiliary inputs**
**Other Numerical Weather Prediction centres**
**Different operational schedule/assimilation strategy**
**Different processing params/aux inputs/algorithms**
**Research institutes & general scientific users**
**Different processing params/aux inputs/algorithms**

## 2a-1. ECMWF “operational” configuration

## 2a-2. ESA-LTA late- and re-processing

## 2a-4. Research/general scientific use

## 2a-3. Other NWP configurations

## 2b.  Why distribute L2BP Source Code?

**Distribution of executable binaries only permits**
**limited number of computing platforms**
**different settings in processing parameters input file**
- thresholds for QC, cloud detection
**different auxiliary inputs**
- option to use own meteorological data (T & p) in place of ECMWF aux met data (available from LTA)
**Provide maximum flexibility for other centres/institutes to generate their own products**
**different operational schedule/assimilation strategy**
**scope to improve algorithms**
- feed into new releases of the operational processor

## 3a.  How it works – Tan et al Tellus A in press

**Rayleigh channel HLOS retrieval – Dabas talk**
**R = (A-B) / (A+B) and HLOS = F****-1 ****(R;T,p,s)**
**T and p are auxiliary inputs**
**correction for Mie contamination, using estimate of scattering ratio s**
**Mie channel HLOS retrieval**
**peak-finding algorithm (4-parameter fit as per L1B)**
**Retrieval inputs are scene-weighted**
**ACCD = ****Σ**** ACCD****m**** W****m****, W****m ****between 0 and 1**
**Error estimate provided for every Rayleigh & Mie hlos**
**dominant contributions are SNR in each channel**

## Rayleigh-Brillouin spectrum and Aeolus response curves

**Rayleigh-Brillouin spectrum and Aeolus response curves**

- Rayleigh
- Rayleigh-Brillouin

*R* = *(A-B)/(A+B)*

**Dabas et al., Tellus accepted**

**3b. Level-2B input screening & feature finding**

- Poli/Dabas
- Meteo-France

**3b. Level-2B hlos wind retrievals**

- Poli/Dabas
- Meteo-France

## 3b. Level-2B hlos retrieval - error estimates

## 3b. Level-2B hlos retrieval - error estimates

- Poli/Dabas
- Meteo-France

## 3c.  Future work

**Quality Indicators**
**Highlighting doubtful L2B retrievals**
- More complicated atmospheric scenes from simulations + Airborne Demonstrator
**Advanced feature-finding/optical retrievals**
**Methods based on NWP T & p introduce error correlations**
**Modified measurement weights**
**More weight to measurements with high SNR?**
**Height assignment**
**In situations with aerosol and vertical shear**

## 4.  Distribution of L2BP software

**Software releases issued by ECMWF/ESA**
**Details & timings to be determined **
**Probably via registration with ECMWF and/or ESA**
**Source code and scripts for installation**
- Fortran90, some C support
- Developed/tested under several compilers
**Suite of unit tests with expected test output**
**Documentation**
- Software Release Note
- Software Users’ Manual
- Definitions of file formats (IODD), ATBD, etc.

## Observation Processing
Data Flow at ECMWF

**Data Flow at ECMWF**

- Non-IFS processing

- Observation Screening

- Assimilation Algorithm

- Diagnostic post-processing

- “Bufr2ODB”
- Convert BUFR to ODB format
- Recognize HLOS as new known observable

- IFS “Screening Job”
- Check completeness of report, blacklisting
- Background Quality Control

- IFS “4D-VAR”
- Implement HLOS in FWD, TL & ADJ Codes
- Variational Quality Control

- “Obstat” etc (Lars Isaksen)
- Recognize HLOS for statistics
- Rms, bias, histograms

*Level-1B data*
*(67 1-km measurements)*

*Analysis*

**Assimilation of prototype ADM-Aeolus data****Reception of L1B data and L2B processing at NWP centres**

*L2BP (1 50-km observation)*

## 5.1 Prototype Level-2C Processing

**Ingestion of L1B.bufr into the assimilation system**
**L1B obs locations within ODB (internal Observation DataBase)**

**Assimilation of HLOS observations (from L1B)**
**Corresponding analysis increments (Z100)**

## 5.2 Key assimilation operators

**HLOS, TL and AD**
** ****H ****	****	****=    -  u sin ****φ****  -  v cos ****φ**
**dH ****	****	****=    - du sin ****φ****  - dv cos ****φ**
**dH*****	****	****=  ( - dy sin ****φ****, - dy cos ****φ**** )****T**
**Generalize to layer averages later**
**Background error**
**Same as for u and v (assuming isotropy)**
**Persistence or representativeness error**
**10 to 20 m/s for technical development**
**Prototype quality control**
**Adapt local practice for u and v**

## Slide 22

## Profiles of 12-hr Fc impact, Southern Hemisphere

**Profiles of 12-hr Fc impact, Southern Hemisphere**

**Spread in zonal wind (U, m/s)**
**Scaling factor ~ 2 for wind error**
**Tropics, N. & S. Hem all similar**
**Simulated DWL adds value at all altitudes and in longer-range forecasts (T+48,T+120)**
**Differences significant (T-test)**
**Supported by information content diagnostics**

- Pressure (hPa)

- Zonal wind (m/s)

## 5.3 L2BP integration within an assimilation system

- ODB

**4DVar**

**5.3 L2BP integration within an assimilation system**

- screening

- Background   T p

- L1B-odb             lat lon

-                            AMD-odb

- Background hlos

- L2B-odb

- Obs - Bg, BgQC, etc

- L2B Processor

- L1B%  AMD%

- L2B%

- Wrapper module copies “odb” variables to & from % data structures
- (hidden from screening)
- C.f. RTTOV + SSMI
- TCWV

## 5.4 Overview data flow – standalone mode

- AMD

- L2B

- L1B

**5.4 Overview data flow – standalone mode**

- EE

- L2BP_standalone

- L2B Processor

- L1B%  AMD%

- L2B%

## 5.5 Principal Guidance to Met Centres

**How to install and test the standalone version**
**Source code, documentation, unix scripts and test data (EE format) supplied**
**Useful tool for inter-comparison purposes**
**Interface requirements for integrated-assimilation mode**
**Generation of auxiliary meteorological data**
**Wrapper module between “odb” and L2B processor used as a callable subroutine within assimilation.x**
**Both to occur during Screening**
**Facilitates assimilation of Aeolus data**
**Assimilation outputs at discretion of each met centre**