Start Date | Start Time | End Date | End Time | Data Quality Metric |
---|---|---|---|---|
04/01/1994 | 0000 | 04/09/1996 | 2359 | Suspect |
Subject: | Reprocess: LBLRTM and AERI/LBL QME data |
DataStreams: | sgpqmeaerimeansC1.c1, sgpaerilbldiffC1.c1, sgpqmeaerilblC1.c1, sgplblch2C1.c1, sgplblch1C1.c1 |
Description: | DQR No: Subject: LBLRTM and AERI/LBL QME data Date Submitted: 7/2/96 Submitted By: Tim Shippert ___ Instrument Mentor _X_ EST Member ___ Science Team Member ___ Other _____________________________ Organization: PNNL Email address: tr_shippert@pnl Telephone: 509-375-5997 Platform/Measurement: LBLRTM model runs: sgplblch1C1.c1 sgplblch2C1.c1 AERI/QME output: sgpqmeaerilblC1.c1 sgpqmeaerimeansC1.c1 sgpaerilbldiffC1.c1 What level data: (raw,a0,a1,b1,c1 etc): c1 What location was the data collected at: SGP Period of time in question Begin Date 4/1/94 End Date current Data should be labeled: ___ questionable ___ incorrect ___ wrong calibration _X_ other: Usefulness of data is limited to instrument validation and the evaluation of atmospheric state measurements, and should not be used for the study of radiative transfer modeling issues Discussion of Problem: The AERI/LBLRTM QME, which compares the output of the Line by Line Radiative Transfer Model (LBLRTM) with the spectra measured by the Atmospheric Emitted Radiance Interferometer (AERI) at the SGP CART Central Facility, has been successful in identifying and assessing problems with the measurement of downwelling spectral radiation and the characterization of the atmosphere in the radiating column, but there are serious concerns regarding the use of this data for understanding and addressing radiative transfer modeling issues by the scientific community. There are three main purposes of the QME: (1) To improve modeling of radiative transfer; (2) To assess the ability to measure high-resolution downwelling radiation, in particular from the AERI instrument; (3) To assess the ability to characterize the atmosphere in the radiating column, including water vapor. The AERI/LBL QME has been instrumental in finding numerous problems with (2) and (3), as seen in the attached timeline. Because the AERI and sonde data are being released, it is important to identify issues related to these datasets, which can be accomplished using the AERI/LBLRTM QME. Therefore, the QME is a useful tool for validating and establishing data quality for the instrument data streams. As a result the QME process, difficulties associated with ARM-style automated data collection are identified. Because of the difficulties associated with the measurement of spectral radiance and, most importantly, that characterization of water vapor as part of the atmospheric state, the QME has been unable to contribute to the improvement in radiative transfer modeling. Therefore, the QME data should not be used as a basis for improvements to radiative transfer models; the magnitude of the residuals due to errors in the determination of the atmospheric path in the radiating column are larger than those due to modeling error. The following are periods of time which may be used for general analyis of spectral radiance measurements: (a) 5/94-12/94 This period was prior to the time period which has been identified as containing radiosonde launches with the Vaisala sonde calibration problem. The AERI00 data has been reprocessed to correct for the field of view obscuration. However, pseudo-Vaisala processing of sonde data was used through 5/21/94. Therefore, the model validations and the associated QME data should be treated seperately from other time periods. (b) 7/95-8/95 This period was prior to the time in which the dust on the AERI01 mirror impacted the data. Some sondes during this period have the Vaisala correction problem, which are identifiable using serial numbers. The MPL data is questionable due to issues of dust and wear, which impacts the ability to determine clear sky cases. (c) 1/96-3/96 The mirror on the AERI01 was replaced, but the data quality is currently unknown. The MPL00 data has the same problems as in (b). Most importantly, the MWR was not running during this period, so we have no comparisons with sondes and our ability to detect clouds from liquid water is limited. (d) recent data from 4/96 on A new "improved" mirror was put in the AERI01 in April '96 (data quality still unknown, however), and the MPL02 came on line in May. Data from this period looks good; however it has not been as throroughly analyzed as older data, and potential problems have not had as much time to surface. ----- The following paragraphs summarize the problems and issues with the instrument datasets related to the LBLRTM model runs. AERI ---- The sporadic LN2 loss in the AERI00 dewar from April, 1994 through July 25, 1995 is manifested in the gradual increase in noise into the AERI00 measured spectrum, ultimately manifested by a Planck function spectrum of the detector temperature as the detector warms upon running out of the N2 coolant. These spectra were included in the data distribution of the AERI00 spectra as well as the QME validations with LBLRTM, although during subsequent reprocessing caused by the FOV problem (see next paragraph) these samples have been flagged in the AERI data and skipped by the QME. The current AERI01 instrument makes use of a stirling cooler and no longer requires an LN2 dewar. The field of view of the AERI was partially obscured from April, 1994 through July 6, 1995, which resulted in a several percent increase on measured radiance [Knuteson, et al., 1995]. The effect of this obstruction has been removed from the spectral measurements, and both the AERI and AERI/LBLRTM QME data has been reprocessed and redistributed. Use of the original, uncorrected data is not advised. The accumulation of dust on the AERI01 collection mirror over the period 9/1/95 through 12/22/95 resulted in an obscuration which may be similar in nature to that of the AERI00 obstruction. A similar effect has been identified over the period 1/18/96-4/9/96. The data has not been corrected, although efforts are underway to remove the effect of the dust from the radiance spectra. It is advised that the AERI01 data over these time periods not be used for scientific study prior to reprocessing (see AERI DQR #'s P960715.1 and P960715.2). MWR --- Other measurement datasets related to the AERI/LBLRTM QME studies have been identified as having problems in certain time periods. Temperature calibration issues in the MWR from 4/94 through 12/94 are being addressed, though the data which is currently released reflects incorrect calibration coefficients. The processing of MWR measured brightness temperatures in the retrieval of total water vapor and total liquid water has changed starting 3/1/96, which has resulted in improved agreement between the column water vapor product from the MWR platform and the retrieved total water vapor which is done as part of the MWR/LBLRTM QME in conjunction with the AERI/LBLRTM QME. BBSS ---- The AERI/LBLRTM QME studies have identified several issues with the radiosonde data. The nominal Vaisala processing of the raw radiosonde data from 4/94 through 5/21/94 was not done, which resulted in the use of the unprocessed data in the validations of the line by line model with the radiance measurements and release of QME data. The radiosonde data was subsequently processed using software written at PNL which intended to mimick the Vaisala proprietary alogrithms, and the validations and QME products were rerun. The model calculations and QME data for this time period should be treated distinctly from those of subsequent time periods as a result of the differing radiosonde processing software. From 4/94 to 8/3/94, ground checks were routinely applied to nominal BBSS PTU data. These ground checks were removed before using the data as input to the LBLRTM. From 4/94 through 5/21/94, the period described in the above paragraph, ground checks were removed as part of the pseudo-Vaisala processing. From 5/21/94 to 8/3/94, the ground checks were removed from the Vaisala nominal data by a seperate post-ingest routine. After 8/3/94, ground checks were no longer applied to nominal BBSS data. Over the time period of 1/20/94 through 9/22/95, some radiosondes launched were incorrectly calibrated by Vaisala at the factory and incorrectly measured water vapor through the atmosphere. This data, including the model validations and QME products, cannot be corrected and should not be used. For more information, including the serials numbers of those sondes affected, refer to the DQR submitted 2/28/96 by Barry Lesht, the instrument mentor. In addition, some studies [Clough et al., 1996; Whitney et al., 1996] have indicated that the radiosonde measurements contain systematic errors in observing water vapor through the atmospheric path, and that these errors are the largest source of disagreement between the line by line model and the spectral radiance measurement. ---- The following is a timeline of most of the data streams related to the AERI/LBL QME. It graphically illustrates just how many things can affect the QME. The timeline table is 172 columns wide, so you will probably need to resize your window or print it out in landscape mode to see it completely: ARM AERI/LBLRTM QME Timeline MPL00 Era MPL02 Era _____________________________________________________________|____________________________________________________________________________________________ ____|____ | | | MWR in datastream (S/N 010) MWR in datastream _________________________________________________|_______________________________________________________________ ______________________|___________ | | | AERI01 Era AERI00 Era _ _ _ _ _ _ _ _ _ _ _ _ _______________________________________|__________________________________________________________________ _________________________________|____|________________________|_______ | | 4/94 12/94 4/17/95 5/7/95 7/6/95 7/31/95 9/1/95 10/95 12/1/95 1/18/96 3/15/96 4/16/96 5/10/96 |-----|----/-----|------|-------|------|-------|-------|--------|-------|-----|------|-----|------|------|---|----|----|-------|-------|-------|------|----|----|----|---> 5/21/94 1/20/95 4/26/95 5/31/95 7/25/95 8/28/95 9/22/95 11/1/95 12/22/95 3/1/96 4/9/96 4/20/96 |______________| |___________| |__________| |______________| | | | | SCM IOP SCM IOP (7/17-8/6) ARESE IOP (O3 sondes) IOP |_______________________________________________________________________| | Sporadic AERI00 LN2 Dewar fill problem |_______________________________________________________________|__________________________|___________________________|_______|______________________|___________________ | | | | | | AERI00 FOV obscuration (corrected) Mirror #1 Dust on mirror #1 Mirror #2 Residue on mirror #2 Mirror #3 |_____| |_________________________________________________________________________| | | Pseudo-Vaisala Vaisala Calibration Problem (Central Facility) Processing (no correction) |________________| |__________________________________ | | MWR Calibration Problem Change in MWR data product processing (to be reprocessed) |_____________________________________________________________________________________________| | MPL00 Data Questionable (wear/dust issues) References: Knuteson, R., B. Whitney, H. Revercomb, & F. Best. (1995). The history of the University of Wisconsin Atmospheric Radiance Interferometer (AERI) prototype during the period April 1994 through July 1995. (Technical Report with ARM PIF #'s P950525.4 and P950224.1). University of Wisconsin-Madison. Clough, S.A., P.D. Brown, J.C. Liljegren, T.R. Shippert, & D.D. Turner. (1996) Implications for atmospheric state specification from the AERI/LBLRTM QME and the MWR/LBLRTM QME. Proceedings of the Sixth Atmospheric Measurement Program (ARM) Science Team Meeting. Whitney, B.A., H.E. Revercomb, R.O. Knuteson, F.A. Best, and W.L. Smith. (1996). Atmospheric Emitted Radiance Interferometer (AERI), part II: Water vapor and atmospheric aerosols. Proceedings of the Sixth Atmospheric Measurement Program (ARM) Science Team Meeting. Suggested Corrections of the Problem: AERI/LBL QME Data should be released only with this DQR attached. Tim Shippert tr_shippert@pnl.gov (509) 375-5997 FAX: (509) 375-3641 |
Suggestions: | AERI/LBL QME Data should be released only with this DQR attached. |
Measurements: | sgpqmeaerilblC1.c1: more
sgplblch2C1.c1: more sgplblch1C1.c1: more sgpaerilbldiffC1.c1: more sgpqmeaerimeansC1.c1: more |