LIS/OTD 2.5 Degree Low Resolution
Diurnal Climatology (LRDC)
1. Name
LIS/OTD 2.5 Degree Low Resolution
Diurnal Climatology (LRDC)
2. Version
v2.2
3. Short Description
The product is a 2.5 deg x 2.5 deg gridded
composite of climatological total (IC+CG) lightning bulk production as
a function of local hour, expressed as a flash rate density (fl/km2/hr).
Climatologies from the 5-yr OTD (4/95-3/00) and 8-yr LIS (1/98-12/05)
missions are included, as well as a combined OTD+LIS climatology and supporting
base data (flash counts and viewing times). Best-available detection efficiency
corrections and instrument cross-normalizations, as of the product generation
date (1/28/06), have been applied.
4. Format
The product is distributed in HDF (Hierarchical
Data Format). HDF is accessible from C or Fortran using interfaces provided
by NCSA (http://hdf.ncsa.uiuc.edu),
or through various commercial software packages, such as IDL or Noesys
(http://www.rsinc.com). All data in this product are stored in HDF Scientific
Data Sets (SDS).
5. Citation
and Acknowledgements
In presentations or publications, users
are to acknowledge the dataset as follows:
The v2.2 gridded satellite lightning
data were produced by the NASA LIS/OTD Science Team (Principal Investigator,
Dr. Hugh J. Christian, NASA / Marshall Space Flight Center) and are available
from the Global Hydrology Resource Center (http://ghrc.msfc.nasa.gov).
6. Long Description
- NOTE: Version 2.2 release included new documentation in PDF format, which can be viewed and downloaded here:
ftp://ghrc.nsstc.nasa.gov/pub/doc/lisotd_gridded_products/lis_otd_gridded_products_documentation_v2.2.pdf
- Approach
Bulk lightning
production, expressed in fl/km2/hr, is calculated as a "counting
experiment", i.e., all flashes observed during each local hour
by the sensors in a given grid location are summed for the full period
considered
(OTD, 5 yr; LIS, 8 yr), then divided by the actual instrument viewing
time of the grid location. Flashes are weighted during the summation
by the
best instantaneous estimate of each instrument’s flash detection efficiency
(DE); e.g., if the DE estimate is 50%, a value of 2.0 is added to the
flash summation grid. Instrument viewing dropouts due to temporary
platform or
instrument down-time are considered. Partial grazing of a grid location
by the instrument FOV is considered in the LIS estimates, but not considered
in the OTD estimates. Best available DE corrections are applied as
a function of instrument, local hour, and for the OTD, spatial location
(see below).
The combined flash rate climatology merges the corrected OTD and LIS
climatologies to reduce variance in the tropical estimates.
- Contents
The HDF file
contains 12 Scientific Data Set (SDS) grids. These include:
- LRDC_COM_FR Combined
Flash Rate [24x144x72, float, fl/km2/yr]
- LRDC_OTD_RF OTD
Raw Flashes [24x 144x72, float, flashes]
- LRDC_OTD_SF OTD
Scaled Flashes [24x 144x72, float, flashes]
- LRDC_OTD_VT OTD
Viewtime [24x 144x72, float, km2-sec]
- LRDC_OTD_FR OTD
Flash Rate [24x 144x72, float, fl/km2/hr]
- LRDC_LIS_RF LIS
Raw Flashes [24x 144x72, float, flashes]
- LRDC_LIS_SF LIS Scaled
Flashes [24x 144x72,
float, flashes]
- LRDC_LIS_VT LIS Viewtime [24x
144x72, float, km2-sec]
- LRDC_LIS_FR LIS Flash
Rate [24x 144x72,
float, fl/km2/hr]
- LRDC_OTD_DE OTD
Detection Eff. [144x72x24x3, float, %]
- LRDC_LIS_DE LIS Detection
Eff. [144x72x24,
float, %]
- LRDC_AREA Grid
cell areas [144x72, km2]
Of these, LRDC_COM_FR is the primary data
product; the combined LIS/OTD flash rate (FR) climatology. It may derived
as: LRDC_COM_FR = (LRDC_OTD_SF + LRDC_LIS_SF) / (LRDC_OTD_VT + LRDC_LIS_VT)
(for nonzero total viewing time grid cells). The supporting base grids (raw
flash counts RF, detection efficiency-scaled flash counts _SF, and
total viewing _VT) are provided only for reference or rebinning. Users are
encouraged to view the viewing grids to understand the nature of the Low
Earth Orbit satellite sampling, which is a component of the uncertainty at
each grid location. The diurnally-applied detection efficiency corrections
are also included (_DE; see below). A grid cell area (_AREA) product is also
included, to simplify net production calculations (e.g., global annual production
in fl/sec = sum(LRDC_COM_FR * LRDC_AREA)).
The dimension scales accompanying the SDS
grids represent the center coordinate of each 2.5 degree grid cell
(e.g., -178.75, -176.25 … 176.25, 178.75 deg lon, etc.) and local hour (e.g.,
0.5 … 23.5).
- Calibration
Best-available calibrations for instrument
detection efficiency (as of 1/28/06) have been applied in the v2.2 product.
These consider variations in instrument sensitivity across the angular field
of view, variability in the background scene radiance (the instruments are
designed to reduce sensitivity as background radiance increases in order
to preserve signal-to-noise ratio), actual cross-sensor ground validation,
and cross-normalization of climatological results between the two instruments.
The procedure, which is being documented for publication in J. Atmos.
Oc. Tech., is roughly as follows:
- The diurnal distribution of cloud background radiance
(upon which sensitivity depends) is estimated from LIS background scenes
concurrent with lightning events [Boccippio et al, JAOT, in review].
- Laboratory calibration data [Koshak et al, 2000] are
used with (1) to estimate the diurnal distributions of minimum detectable
pixel radiance.
- A pre-launch Optical Pulse Sensor (OPS) data base
of pulse radiance distributions acquired from high altitude (U2) airplane
measurements [Christian and Goodman, 1987] are used with (2) to predict
the diurnal distribution of maximum possible LIS and OTD flash detection
efficiency (following and expanding upon [Koshak et al, 2000]). The OTD
prediction is computed for threshold settings used from 10/23/96-4/1/00.
- The LIS nighttime flash detection efficiency is estimated
to be 88%, based on ground validation by [Thomas et al, 2000] and [Koshak
et al, AGU Fall Meeting, 2000]. The LIS maximum possible flash detection
efficiency diurnal distribution is scaled by this value.
- The results of (3) and the uncorrected climatological
data yield a LIS:OTD flash detection efficiency ratio of 1.67 [Boccippio
et al, JAM, 2000; Boccippio et al, JAOT, in review]. The OTD maximum
possible nighttime flash detection efficiency is set to (1/1.67)*0.88,
and the OTD predicted diurnal flash detection efficiency cycle from (3)
is scaled accordingly.
- The OTD diurnal flash detection efficiency cycle during
other threshold setting windows (04/01/95-06/09/95, 06/09/95-07/20/95,
07/20/95-10/23/96, 10/23/96-04/01/00) is adjusted slightly by relative
differences determined from ground validation [Boccippio et al, JAOT,
2000]. Three grids are reported in the file; these date windows use grids
(0,2,1,0) respectively.
- The OTD flash detection efficiency over South America
is further scaled using the climatological ratio of LIS to OTD detections.
OTD flash detection efficiency in this region drops within the South
Atlantic Anomaly as adaptive software noise filters are more active to
remove radiation noise events in the CCD pixel array. The peak reduction
in DE from this effect is estimated to be an additional 50%, centered
over Sao Paulo, Brazil.
Detection efficiency adjustments are thus
prescribed as a function of (sensor, longitude, latitude, local hour, date
in mission [OTD only]). These are included, for reference, in the HRFC_OTD_DE
and HRFC_LIS_DE Scientific Data Sets. The bulk effect of the instantaneous
corrections can be estimated as: BULK_OTD_DE = sum(HRFC_OTD_RF) / sum(HRFC_OTD_SF)
(~ 49%) or BULK_LIS_DE = sum(HRFC_LIS_RF) / sum(BULK_LIS_SF) (~ 82%).
Users wishing to cite this calibration
procedure may use or modify the following:
Observations in the LIS/OTD v2.2
reanalysis have been corrected by the LIS Science Team by estimated
flash
detection efficiency, applied as a function of sensor, local hour, date
of mission, and (for the OTD) geographic location. For the entire dataset,
these corrections correspond to average flash detection efficiencies of
49% (OTD) and 82% (LIS). The adjustments derive from a combination of laboratory
calibration, ground-validation, and cross-normalization between the two
instruments. Uncertainty in these corrections is estimated as +/- 10%.
The calibration procedure is described in the dataset documentation.
- Uncertainty
Consistency between modeled and ground-validated
detection efficiency suggests that the applied values are known within about
+/- 10%. This is thus the minimum uncertainty in the gridded data, arising
from possible bias in the correction. Local variance arises from undersampling
of a given grid location, and its relative impact increases as the actual
local climatological flash rate decreases. This effect is likely dominant
in the LRDC, but less important in the LRDC. During the 3rd-5th years
of the OTD mission, problems with the host platform caused observations near
local noon and midnight to be preferentially lost. In the combined diurnal
climatology, early morning and mid-afternoon hours are thus sampled slightly
(~15%) more than local midnight and noon. The effect in the diurnal decomposition
is thus nonuniform variance in the hourly estimates, not a bias.
The primary error sources (measurement
uncertainty, sampling-related variance) are currently being quantified.
- Quality Assurance
All
OTD and LIS orbits undergo both automated and manual quality assurance.
For the preliminary
reanalysis, the most stringent
orbit rejection criterion was applied: any orbit which was assigned a manual
Q/A "warning" flag has been rejected from the reanalysis. In
subsequent versions, these rejected orbits may be examined individually
and, if acceptable,
added into the climatology to improve sampling.
Each
OTD flash is further assigned an automated quality index (the
‘Thunderstorm Area Count’,
or ‘Density Index’), indicating
its likelihood of being lightning rather than optical or radiation
noise. For this reanalysis, only flashes with values of the metric >=
140 have been included. This is the same cutoff value used in all validation
and science
analysis published by the LIS science team to date. This filter
removes most radiation noise from the climatology; a slight residual
‘ring’ artefact
of
very low spurious flash rates remains at the periphery of the South
Atlantic Anomaly (southeast Pacific and southeast Atlantic).
7. Recommended Usage
There are no restrictions on the use
of these data. While best-available instrument
calibrations have been applied, there are several known performance and
algorithm issues still being addressed, and the applied calibrations have
not yet been fully peer-reviewed and documented in refereed journals (see
section 6). The data are best used for examination of relative diurnal
and spatial variability. Further bias adjustments to the applied detection
efficiencies will likely occur in the near future, and result in product
version updates (see section 8).
Sampling in the Low Resolution diurnal
climatology should be adequate to resolve broad regional trends in the
phase and amplitude of the diurnal cycle. However, the diurnal cycle estimates
for individual grid cells are fairly noisy and undersampled, so aggregation
of data from several grid cells is recommended. As with the high resolution
flash rate climatology, it is recommended that the individual scaled flashes
(_SF) and viewtime (_VT) grids be aggregated separately, then divided,
to yield lower resolution flash rate estimates; this is preferable over
simple averaging of adjacent 2.5 degree flash rate (_FR) grid cells.
8. Versioning
and Updates
All subsequent
versions of this dataset (both minor and major revisions) will maintain
the same product definition,
resolution and file format. Additional years of data from the LIS mission
may be added into the climatology for future revisions, but will not
alter file format. Any actual definitional changes would be reflected by
the
creation of a new product.
The current product
version is v2.2. Users may request notification of updates from the Global
Hydrology Resource Center. Subsequent major version updates will only
occur if/when the dataset is recomputed using new major version OTD or
LIS orbit
data. E.g:
Status OTD
Orbit Version LIS Orbit
Version LRDC Version
Preliminary 1.1 4.0 0.x
Peer-reviewed 1.1 4.0 1.x
Subsequent 2 or higher
OR 5 or
higher 2.x, 3.x,
9. References
Instrument and Calibration/Validation:
Goodman,SJ; Christian,HJ; Rust,WD
(1988): A comparison of the optical pulse characteristics of intracloud
and cloud-to-ground lightning as observed above clouds. J. Appl. Met.
27, 1369-1381.
Christian,HJ; Blakeslee,RJ; Goodman,SJ
(1989): The Detection of Lightning from Geostationary Orbit. J. Geophys.
Res. 94, 13329-13337.
Christian,HJ; Blakeslee,RJ; Goodman,SJ
(1992): Lightning imaging sensor for the Earth Observing System. (TM-4350.)
NASA. 44 pages. Available from Center for Aerospace Information, P.O.
Box 8757, Baltimore Washington International Airport, Baltimore, MD 21240.
Christian,HJ; Driscoll,KT; Goodman,SJ;
Blakeslee,RJ; Mach,DA; Buechler,DE (1996): The Optical Transient Detector
(OTD). Proc. 10th International Conference on Atmospheric Electricity,
Osaka, Japan.
Kummerow, C; Barnes, W; Kozu,
T; Shiue, J; Simpson, J (1998): The Tropical Rainfall Measuring Mission
(TRMM) sensor package. J. Atmos. Oc. Tech. 15, 809-817.
Christian,HJ; Blakeslee,RJ; Goodman,SJ;
Mach,DA; Stewart,MF; Buechler,DE; Koshak,WJ; Hall,JM; Boeck,WL; Driscoll,KT;
Boccippio,DJ (1999): The Lightning Imaging Sensor. Proc. 11th Intl. Conf.
on Atmospheric Electricity (NASA), Guntersville, AL, 7-11 June. 746-749.
Ushio,T; Driscoll,KT; Heckman,S;
Boccippio,DJ; Koshak,WJ; Christian,HJ (1999): Initial comparison of the
Lightning Imaging Sensor (LIS) with Lightning Detection and Ranging (LDAR).
Proc. 11th Intl. Conf. on Atmospheric Electricity (ICAE), Guntersville,
AL, 6-11 June. 738-741.
Christian,HJ; Blakeslee,RJ; Goodman,SJ;
Mach,DM (eds.) (2000): Algorithm Theoretical Basis Document (ATBD) for
the Lightning Imaging Sensor (LIS). Posted:
1 Feb 2000. (NASA / Marshall Space Flight Center, AL 35812)
Koshak,WJ; Bergstrom,JW; Stewart,MF;
Christian,HJ; Hall,JM; Solakiewicz,RJ (2000): Laboratory calibration
of the Optical Transient Detector and Lightning Imaging Sensor. J. Atmos.
Oc. Tech. 17, 905-915.
Boccippio,DJ; Driscoll,KT; Koshak,WJ;
Blakeslee,RJ; Boeck,WL; Mach,DA; Buechler,DE; Christian,HJ; Goodman,SJ
(2000): The Optical Transient Detector (OTD): Instrument characteristics
and cross-sensor validation. J. Atmos. Oc. Tech. 17, 441-458.
Thomas,RJ; Krehbiel,PR; Rison,W;
Hamlin,T; Boccippio,DJ; Goodman,SJ; Christian,HJ (2000): Comparison of
ground-based 3-dimensional lightning mapping observations with satellite-based
LIS observations in Oklahoma. Geophys. Res. Lett. 27, 1703-1706.
Boccippio, DJ; Koshak, WJ; Blakeslee,
RJ (2001): Performance assessment of the Optical Transient Detector and
Lightning Imaging Sensor: I. Predicted diurnal variability. J. Atmos.
Oc. Tech., submitted (preprint available upon request).
LIS/OTD-Enabled
Science & Applications:
Boccippio,DJ; Wong,C; Williams,ER;
Boldi,R; Christian,HJ; Goodman,SJ (1998): Global validation of single-station
Schumann resonance lightning location. J. Atmos. Sp. Terr. Phys. 60, 701-712.
Christian,HJ; Blakeslee,RJ; Boccippio,DJ;
Boeck,WL; Buechler,DE; Driscoll,KT; Goodman,SJ; Hall,JM; Koshak,WJ; Mach,DM;
Stewart,MF (1999): Global frequency and distribution of lightning as
observed by the Optical Transient Detector (OTD). Proc. 11th Intl. Conf.
on Atmospheric
Electricity (ICAE), Guntersville, AL, 7-11 June. 726-729.
Driscoll,KT (1999): A comparison
between lightning activity and passive microwave measurements. 11th International
Conf. on Atmospheric Electricity (ICAE), Guntersville, AL, 7-11 June
1999. 523-526.
Cecil, DJ; Zipser, EJ (2000):
Relationships between tropical cyclone intensity and satellite-based
indicators of inner core convection: 85 GHz ice-scattering signature and
lightning.
Mon. Wea. Rev., 111, 979-996.
Buechler,DE; Driscoll,KT; Goodman,SJ;
Christian,HJ (2000): Lightning activity within a tornadic thunderstorm
observed by the Optical Transient Detector (OTD). Geophys. Res. Lett
., 27, 2253-2256.
Goodman,SJ; Buechler,DE; Knupp,K;
Driscoll,KT; McCaul,EW (2000): The 1997-98 El Nino event and related
wintertime lightning variations in the Southeastern United States. Geophys.
Res. Lett.
27, 541-544.
Jeker,DP; Pfister,L; Thompson,AM;
Brunner,D; Boccippio,DJ; Pickering,KE; Wernli,H; Kondo,Y; Staehelin,J
(2000): Measurements of nitrogen oxides at the tropopause: Attribution
to convection
and correlation with lightning. J. Geophys. Res., D 105, 3679-3700.
Boccippio,DJ; Goodman,SJ; Heckman,S
(2000): Regional differences in tropical lightning distributions. J.
Appl. Met. 39, 2231-2248.
Williams,ER; Rothkin,K; Stevenson,D;
Boccippio,DJ (2000): Global lightning variations caused by changes in
thunderstorm flash rate and by changes in the number of thunderstorms.
J. Appl. Met.
39, 2223-2230.
Nesbitt,SW; Zipser,EJ; Cecil,DJ
(2000): A census of precipitation features in the tropics using TRMM:
Radar, ice scattering and lightning observations. J. Clim. 13, 4087-4106.
Rodgers, E; Olson, W; Halverson,
J; Simpson, J; Pierce, H (2000): Environmental forcing of supertyphoon
Paka’s (1997) latent heat structure. J. Appl. Met., 39, 1983-2006.
Boccippio,DJ; Cummins,KL; Christian,HJ;
Goodman,SJ (2001): Combined satellite and surface-based estimation of
the intracloud / cloud-to-ground lightning ratio over the continental United
States. Mon. Wea. Rev. 129, 108-122.
Toracinta, ER; Zipser, EJ (2001):
Lightning and SSM/I ice-scattering mesoscale convective systems in the
global tropics. J. Appl. Met. 40, 983-1002.
Boccippio, DJ; Heckman, S; Goodman,
SJ (2001): A diagnostic analysis of the Kennedy Space Center LDAR network.
2: Cross-sensor studies. J. Geophys. Res. 106, 4787-4796.
Chang, DE;Weinman, JA; Morales,
CA; Olson, WS (2001): The effect of spaceborne microwave and ground-based
continuous lightning measurements on forecasts of the 1998 Groundhog
Day storm. Mon. Wea. Rev., 129, 1809-1833.
Ushio,T; Heckman,S; Boccippio,DJ;
Christian,HJ (2001): A survey of thunderstorm flash rates compared to
cloud top height using TRMM satellite data. J. Geophys. Res., D, accepted.
Boccippio,DJ (2001): Lightning
scaling laws revisited. J. Atmos. Sci. , accepted.
Bond, DW; Zhang, R; Tie, X.; Brasseur,
G.; Huffines, G; Orville, R.E; Boccippio, DJ (2001): NOx production
by lightning over the continental United States. J. Geophys. Res, accepted.
Koike, M.; Kondo, Y.; Akutagawa,
D.; Kita, K.; Nishi, N.; Liu, S.C.; Blake, D.; Kawakami, S.; Takegawa,
N.; Ko, M.; Zhao, Y.; Ogawa, T. (2001) Reactive nitrogen over the tropical
Western Pacific: Influence from lightning and biomass burning. J. Geophys.
Res., submitted.
Christian, HJ et al (2001): Global
frequency and distribution of lightning as observed by the Optical Transient
Detector. J. Geophys. Res., submitted (preprint available upon request).
9. Sample
Code
A set of Interactive Data Language (IDL)
routines to extract and process the LIS/OTD High Resolution Full Climatology
(HRFC), Low Resolution Full Climatology (LRFC), Low Resolution Diurnal Climatology
(LRDC) and Low Resolution Annual Climatology (LRAC) are distributed with
the data. The IDL syntax is roughly similar to C or FORTRAN and, with the
exception of animation code, porting of these routines should be fairly straightforward.
Full documentation can be found in the program files themselves; a summary
is below.
NOTE: These routines are being provided
as a courtesy to the user community. The GHRC and LIS Science Team cannot
guarantee technical support or compatibility with IDL version updates or
platform-specific implementations.
- GETGRID,HDF_NAME,SDS_NAME,GRID,[DIMS,DIMNAMES,DIM0…]
Retrieves a
scientific data set (and optionally, its dimensions) from one of the
HDF climatology files.
Result = LONLAT_TO_XY([LON,LAT],RESOLUTION)
Converts a [lon,lat] pair to a grid [x,y]
index, for a given grid resolution (0.5 or 2.5 deg).
Result = XY_TO_LONLAT([X,Y],RESOLUTION)
Converts an [x,y] index pair to a grid
cell center [lon,lat], for a given grid resolution (0.5 or 2.5 deg)
Result = HRFC_XY_SMOOTH(N_GRIDCELLS,SENSOR_NAME)
Performs a spatial
moving average on the 0.5 deg High Resolution Full Climatology
with size N_GRIDCELLS. This, e.g., can help smooth the values while preserving
high-contrast
information (as compared with the Low Resolution Full Climatology). The
routine loads the needed grids directly from the HDF file.
Result = LRAC_TIME_SMOOTH(N_DAYS,SENSOR_NAME)
Performs a temporal
moving average with an N_DAYS window on the Low Resolution Annual Climatology.
Strongly recommended for all use of this climatology; with N_DAYS
prescribed in multiples of 55 days. The routine loads the needed grids
directly from the HDF file.
Result = LRAC_XY_SMOOTH(OLDGRID,N_GRIDCELLS)
Performs a spatial moving average on the
2.5 deg results of LRAC_TIME_SMOOTH, to improve sampling.
- MAKE_JGR.PRO:
Recomputes
the statistics and graphics used in H.J. Christian et al, "Global frequency and distribution of lightning
as observed by the Optical Transient Detector", submitted to J.
Geophys. Res., to illustrate statistical processing of the climatological
datasets.
MORE_EXAMPLES.PRO:
Renders three versions of the Full Climatology:
the 0.5 degree HRFC, the HRFC smoothed with a 2.5 deg moving average, and
the 2.5 degree LRFC.
- ANIMATE_ANNUAL,XSIZE,YSIZE
Uses the IDL routine XINTERANIMATE to animate
the combined climatology annual cycle, and optionally export the movie to
MPEG. The movie will have pixel dimensions XSIZE and YSIZE.
- ANIMATE_DIURNAL,XSIZE,YSIZE
Uses the IDL routine XINTERANIMATE to animate
the combined climatology local hour diurnal cycle, and optionally export
the movie to MPEG. The movie will have pixel dimensions XSIZE and YSIZE.
10.
Contact Information
Questions regarding
dataset ordering, media issues, file handling or HDF file access (input/output)
should be directed to the Global Hydrology Resource Center (ghrc@msfc.nasa.gov) Questions
regarding the science data processing, including gridding, viewing, calibration
and variance should be addressed to Dennis.Boccippio@msfc.nasa.gov.
Questions regarding the OTD or LIS missions themselves should be addressed
to the OTD/LIS Principal Investigator,Hugh.Christian@msfc.nasa.gov
Data can be ordered
and questions addressed at http://ghrc.nsstc.nasa.gov/.
To order this data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: ghrc@eos.nasa.gov
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