1. [xl WC llIIzl SDC2. Country LJ.S.A/02.*...._...._.............*...3. Institution .@.?D!il.Q4.N . . . . . . . . . . . . . . . . . . . . .4 . nata set or product name G.WF,. WM. k&r.*..

Tilt Sequence Data. . . . . . . . . . . . . . . . . . . . . . . . . ..*..............".. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*...........

I-3. Data Type Code (s) . ..?.6.....................6. Storage media (code) p?!~-""!'":???s!?~?.....

7. DESCRIPTION AXD ORGANIZATION CF THE DATA SET OR PRODUCT -' I

This data set,which was prepared by the Center for Experiment Designand Data Analysis, contains the polar digital tilt-sequence data (normallyone sequence each 15 min) collected with the 2 XOAA C-band radars for the3 ;‘hzsPs r\f G4TE, Each tilt seqL?enc:r includes a base-tilt scan Lollc~edby scans taken at successively higher antenna tilt angles (nominally, 2"tilt increments betG7een scans). Except in those cases whei-e scans aremissing, a sequence includes all scans throtigh either 1) the first tiltangle where all echoes disappear or, if echoes persist, 2) 22o---the n:a?rinumtilt-angle setting used with the KOAA radars. Each scan contains equiva-lent reflectivity factors (dbz's) for 2o x 2 km data bins out to a maximumradar range of 260 km. The intensity resolution is 1 dbz.

(Continuation of the data set or vroduct description is found_

_1_-_-p

8.

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. i., . .* : . : :; :. ., * . -. : .‘,

. . . . . . . . . . . -‘. -’ . *** . . . . !

"DOCLM3!ITATI@N for GATE 3OAA RADAR TILT-SEQUE:<CE DATA"

July 1976

TABLE OF CO:\Z'ENTS

INTRODUCTION AND BACKGROUND

Related DocumentationSynopsis of Data Set

CRITERIA USED TO DELETE OR CORRECT DATA

Data Deletion 2.1Data Correction 2.2Echo Tilt and Quality Codes 2.3

SHIP POSITIONS AND NAVIGATIONAL DATA

"ABSOLUTE" ACCURACY OF REFLECTIVITY DATA

APPE?JDIX A---"Polar Tilt-Sequence Tape Format for GATEDigital Radar Data"

APPMDIX B---"Criteria Used for Scan Deletion"

APPENDIX C---"Echo Tilt and Quality Codes for Header Words14 and 15"

iSECTION i

1. 1

1.11.2 i

2.,

3.

4.

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"Documentation for GATE KOM Radar Tilt Sequence Data"

.l. INTRODUCIIOB .KXD BACKGROUKD

1.1 Ralatei Documentation--In addition to this documentation, users ofthe t-ilt-sequence data sets may find it helpful to r efer to the followindocuments:

a.1 "Documentation for GATESubset," May 1975,

b-1 "Documentation for GATE1976, and

c.> "Documentation for GATE

These 3'documents, hereafter

Oceanographer Radar Raw Digital Data

.

Researcher Radar Plicrofilm," January

NOAA Radar Hybrid Data," June 1976.

referred to as DGORDS, DGRRX,and DGVRHD,respectively, can be obtained from the GATE World Data Center A, NationalClimatic Center, Asheville, fuorth Carolina. DGORDS, DGRRN, and DGXRHDgive, for example, additional information on a> the characteristicsand performance of the systems, b) the field operations and data re-cording, c) the calibration of the radar systems, and d) the dataprocessing.

1.2 Synopsis of Data Set--This data set contains the polar digital tilt-sequence data (normally one sequence each 15 min consisting of a basetilt scan followed by scans taken at successively higher tilt angles)collected with the 2 NOAA C-band radars for the 3 phases of GATE.

Each scan contains equivalent reflectivity factors (db,z's) for2Ox 2 km data bins out to a maximum range of 260 km.resolution is 1 dbz.

The intensityThe raw digital values for the polar data bins

were obtained in real time by usin g a Digital Video Integrator andProcessor (DVIP) --see DGORDS, section 2. The transfer functions thatwere used to convert the raw digital values from the DRIP to reflecti-vities (dbz' s) are given in DGXRHD (section 1.2). Also, the methodused to determine th,e "noise" cutoff level, below which all DVIP in-tegers,were assigned zero, is discussed in section 1.2 of the DGNRHD.

.

If the nZse level cutoff exceeded 10 for the Oceanographer or 12for the Researcher, a code_appears in header word No. 15. A.high"noise" level affects the discernment of light .precipitation areas.

The configuration of the digital polar arrays and the structureof the tape format is given in Appendix A.

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.',s a part of the edit/preprocess step, many of the zero datascans beginning with the fourth tilt angle, were deleted in order toreduce the vo!une of tapes. Also, bad data scans have been deleted whenthey were not correctable. Bad header words and noise in the reflectivityfields have been correcteh when such corrections were feasible. The echo tiltcode and the quality code (APPENDIX C) identify why a tilt sequence wasterminated, the type of corrections that were made to a scan, and, togetherwith the comments included on the inventory sheet, whether problems remainon a scan or within a.sequence. .

2.1 Data Deletion--Corrections consisted of 1) the replacement of badheader words, and/or 2) interpolation to replace strings of spurious dataalong a radial(s).

There were occasional problems with the header digital logic cards,especially for the Researcher radar system. In some instances all or signi-ficant bits in the header words failed to turn on (or off). If the reflect-tivity data were valid, then the cruical header words were reconstructedby considering the chronology of the scans and by referring to the radarmicroJilms. The following words within the first 13 header-words (APPENDIX A)were defined as crucial ones:

Header Kord No. Description

1 Juiian Date2 Greenwich ?!ean Time3 Tilt angle (times 10)6 Ship ID Code9 Range Interval Code11 Final Ship Heading

Intermittently, (particulary with the Researcher radar data) spurioussignals appeared along ont or more radials. These noise signals were manifestedas strings of high reflo-_ctivities monotonically increasing with range.

Bad radials were filled by interpolation if 9 or less bad radialsoccurred within a scan and if no more than 2 bad radials occurred successively.'If tee pumber of bad radials in a scan exceeded these criter.ia, the sdan was

. f *,deleted [APPENDIX B ) . The interpolation ltias performed between the good radialsl&ich bounded the bad one (or two).

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2.3 Echo Tilt and Quality Codes--To facilitate the_----_-____~_-----actions takc!n to process the data, the echo tilt and

interpretation of thequality codes are

given in header words 14 and 15, respectively (APPENDIX C). The quality codes,together with the comments on the inventory sheets, provide a summary of thequality of the scans on each tape. For example, a quality code of 1 appearingi.n header word Ko. 15 identifies that interpolation was used to replace oneor more bad radials. Examination of the inventory sheets shoxs that the tapewith the greatest number of interpolations (ho. 126) has only 3.7 percent ofthe scans with interpolated radials, and one-half of the tapes have no inter-polations. lisually, on those scans requiring interpolation, there were only1 or 2 bad radials.

. .

.

3. SHIP POSITIOKS AND NAVIGATIONAL DATA

The Oceanographer was stationed near position 1 during Phases 1 and 2and position 4 during Phase 3 (see "Report of the Field Phase," GATE ReportNo. 16, GARP Publication Series, ICSU/k!O, p. vi). The Researcher was stationednear position 5 during all 3 phases. Additional information onthe mean shippositions and deviations from the means is given in DGORDS and DGRRM. Also,for applications which require more precise ship positions, the following datasets, which contain navigational data for the KOAA ships, are available fromthe GATE World Data Center'A., National Climatic Center, Asheville, North,Carolina.

a-> U.S.A. Ships, Navigational Data Set--(Magnetic Tapes)--giveslatitude and longitude for any desired time,

b.)- U.S.A. Ships, General (Boom) --(Magnetic Tape)--gives latitudeand longitude every 3 min, and

c-1 GATE NOAA Radar Hybrid >licrofilm Graphics Data--(Xicrofilm)--gives latitude and longitude.evcry 15 min.

4. "ABSOLUTE" ACCURACY OF REFLECTIVITY DATA

The transfer functions used to drive the equivalent reflectivity factors(dbz's) are based on several types of calibrations and intercomparisons (withseveral repetitions of each type), which are all consistent to within a coupleof decibels. However, rainfall rate estimates obtained from the reflectivitiesusing an empiric+ rainfall rate-reflectivity (R-Ze) relationship may be in.error by more than 2'decibels.if the R-Ze-relationship is in'error And unlessrefinements for attenuation and range effects at middle and far ranges areconsidered. The unrefined estimates should-be interpreted as lower limits,since inclusion of the refinements will always yield higher estimates.

.

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APPEKDIX A

Polar Tilt-Sequence Tape Format for GATE Digital Radar Data___-_I---- ---_I____--

Each logical record on a tilt-sequence tape consists of one scan of re-flectivity data plus header information. The blocking factor is eight(8 blocks/logical record) and the records are variably.spanned blocks (VSB) jwritten without format control (binary). Each header and/ordata word is I2 bytes long (IBX half-word integers).

TAPE CONTEST

TYP” Bytes Words

Header

Polar Array

One Scan

32 16

46,800 23,400 I

- --ct---

23,416:. -

With a blocking factor of eight, we have 46,832/8=5854 hesder'andlor datal_ _-. . . uy~es.blac'k, ..Each,blosk.also .contair!s 4..block.Cescr'ipt~~-.~ord.-(B~f~~j...r. ;.: .- - . 0.bytes and 4 Segment Descriptor Word (SDW) bytes. each block(physical record) has a totai of 586.2 bytes,.

Therefore,The tilt-sequence tapes arc

IBM 360 OS generated unlabelled g-track magnetic tapes written at 1600BPI.

A scan consists of a 130 x 1SO polar array. Each data value (data bin)in the polar array covers an "earth" distance (area) equal to 2O x 2 km.The 23,400 words of polar grid data begin with the first range bin (O-2 km,midpoint = 1 km) of the first radial (lo) and proceed radial by radial,130 data bins per radial. . ..

A schematic summarizing the tilt-sequence tape'format is shown in.?igure Al. Table Al gives a description of the contents of the tape,

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t.Figure 1A. Schkmatic of the tilt-sequence tape forma

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Block and SegmentDescriptors

5854 byte:dbz data

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‘&rd No’, t’ _’ .: -I- No.:Bytes Dcscripticn

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Julian Day

Greenwich Mean Time (hours and minutes: hhmm)

Antenna Tilt Angle X 10 (degrees). Because thesquint angle of the, nutating feed horn bn theResearcher radar was locked at 0.5O while insurveillance mode, 0.5O should be added to allResearcher tilt angles. Angles (0) less thanO*C" are recorded as: 360.0"-9, with the leadingdigit omitted.an angle of 0.4

,For example, for the Rescarcllcrwill be recorded as 3,.

2 .

*. 4

.

2 Azimuth (degrees) of the mid-point of the last2' polar increment included in a scan (usually35soj. Because of the csponcnt.i:ll pulse topulse weighting, this value should not be usedfor assigning azimut:hs to the 180 radials in thescnn; rather, the first rndiai sl~ould be assignedlo true north, tile second 3", etc., and the last359O...

5 2 * Ship Ileading (degrees) for preceding rotationof the antenna.

Ship Identification Code--Oceanographer= 4,-Researcher = 1.

Range Delay Code = DVIP processing began at theradar origin-%! all NOM GATE data.

Time Constant Code setting for the exponentialweighting of the p,.Lse to pulse integration.

G 2

.7

8

2

2

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6 .- 6 -, . J.able Ai., (Contin,ued) Summary of the Content of a Tilt-kquence Tape. .

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-.. -~~&yo.‘~. No. Bytes

---w-

a.0 DescriLZion_-- __ .

9 . 2- . Range Interval Code setting for the radialdimension of the polar data bins. :, 1;~ data

: . 3 bins were used for all of GATE.

10 . i 2.$

Sequence Motie Code - - s i g n i f i e s that radar was:

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11 2;

co l l e c t ing datain the tilt-scqucncc mode.

Ship Heading (degrees) at rllc time the beampassed the ship’s bow during tllc koi.lcction clthe scan. This will normally be the mostaccurate estimate of the ship’s heading duringthe collection of the scan.

. l-2-13 ‘ 4

14 2

Switches used for quality control during pro-cessing.

Echo Tilt Code--See APPENDIX C*. IL, . 15 2 ,

PQuality Code-- ” ” ”

1 16 2 Scan CounterJ‘. 17-2927 5822 dbz Data

/// . Record Gap.*

.8 BDW & SDW

2928-5854 5854 dbz Data

//I

5855-8781-.

.8

5854.

Record Gap

BDW & SDW

dbz Data

._ -~ .____L__.. ._ . . . . _ _ . . _ , ,... .._. .--.- . . . . . . -. ._ -._ __.___.--_I__.

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APPENDIX B

CRITERIA USED FOR SCAN DELETION- -

If visual inspection of compacted B-scans indicated two successivezero data scans above the second tilt, the second zero data scanand all scans above it were deleted. If available, the lowest 3scans were always retained.

All higher tilts following more than 2 successive missing orbad tilts (beginning with the first bad tilt) normally weredeleted, even-when the tilts were missed (or bad) before zero---_data scans were encountered. The base, 2', and 4O tilt scanswere always retained when all 3 were available. The entiretilt sequence was deleted if both the base and the 2O tilt scanswere missing. If the base-tilt scan was present but both the2O and the 4O scans were missing, only the base-tilt scan wasretained, and the remainder of the tilt sequence was deleted.In this case, the base-tilt scan was assigned an echo tiltcode of 1 (see APPENDIX C).

A scan(s) was deleted if data were noisy on 10 or more radialsin the scan.

A scan(s) was deleted if data were noisy on parts or.all ofmore than 2 successive-radiais.

A scan(s) was deleted if crucial header words were missing andcould not be reconstructed from other sources (e.g. microfilm).

Because of..an antenna stabilization problem the OCEMOGRAPHER's .radar data from 0015 GXT day 251 until the end of Phase III can-not be used for 3-dimensional analyses. However, the first fourtilt-angle scans in a sequence were retained for the constructionof a mean hourly hybrid scan. All scans higher than the fourthtilt angle were deleted.

f,.

-3% I_.

APPEXDIX c

ECHO TILT and QI.!ALITY CODES for HEADER I:'ORDS 14 and 15_---

:ho Tilt Code (word 14):1. EC

Code- - Condition

0 --

1 --

Tilt sequence terminated at 22O, or at lower antenna tjlt-anglebecause zero data are observed above the low2r tilt-angle.

Tilt sequence terminated because scans were missing forhigher tilts. Echoes still present on'last available scan.

2. Quality Code (Word 15):

Code

0 --

1 --

2 _-

0. .

4 --

. .

8 --

16 --

nil --

.. .

. I

All normal.

Condition

'Interpolation applied for bad radials.

Header words reconstructed. May be coded in base-tilt headeronly, albeit header corrections were required for other

.tilt'scans kn th6 sequence. ..

DVIP noise level cutoff exceeded 10 forRESEXRCHER.

Azimuth of final radial other than 358'ing azimuth interval: 3503. - 3640,

.

OCEANOGRAPHER or

but falls within

12 for

follow- ,

. . ._’ .,,

Suspected noisy data points within the'tilt sequence (this codeapplies to part or all of a tilt sequence but was coded inthe base-tilt header only).-.

Two or more of the above 5 non-normal conditions existed, wllere nnequals the sum.of the individual codes.

.

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