Survey lines along which EdgeTech SB-512i chirp seismic-reflection data were collected by the U.S. Geological Survey offshore of Massachusetts within Vineyard Sound by the U.S. Geological Survey in 2009, 2010, and 2011 (VS_SeismicTrackline, ESRI Shapefile, Geographic, WGS84).

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   U.S. Geological Survey, 2012, Survey lines along which EdgeTech SB-512i chirp seismic-reflection data were collected by the U.S. Geological Survey offshore of Massachusetts within Vineyard Sound by the U.S. Geological Survey in 2009, 2010, and 2011 (VS_SeismicTrackline, ESRI Shapefile, Geographic, WGS84).: Open-File Report 2012-1006, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

   Online Links:

   • https://doi.org/10.3133/ofr20121006
   • http://pubs.usgs.gov/of/2012/1006/GIS/shapefile/VS_SeismicTrackline.zip
   • http://pubs.usgs.gov/of/2012/1006/appendix.html

   This is part of the following larger work.
   Andrews, Brian D., Ackerman, Seth D., Baldwin, Wayne E., Foster, David S., and Schwab, William C., 2012, High-Resolution Geophysical Data From the Inner Continental Shelf at Vineyard Sound, Massachusetts.: Open-File Report 2012-1006, U.S. Geological Survey, Reston, VA.

   Online Links:

   • http://pubs.usgs.gov/of/2012/1006/

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -71.028834
   East_Bounding_Coordinate: -70.431711
   North_Bounding_Coordinate: 41.548081
   South_Bounding_Coordinate: 41.271214
   

3. What does it look like?

   http://pubs.usgs.gov/of/2012/1006/GIS/browse_jpg/VS_SeismicTrackline.jpg (JPEG)

   EdgeTech 512i trackline navigation offshore of Massachusetts within Vineyard Sound

4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 02-Jun-2009

   Ending_Date: 17-May-2011

   Currentness_Reference:

   ground condition of individual surveys on the following dates: 2009062-20090603; 20100521-20100604; 20110507-20110509; 20110514-20110517

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: vector digital data
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String (399)
   2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.
      
7. How does the data set describe geographic features?

   VS_SeismicTrackline

   Trackline for seismic profiles (Source: USGS)

   FID

   Internal feature number (Source: ESRI) Sequential unique whole numbers that are automatically generated

   Shape

   Feature geometry. (Source: ESRI) Coordinates defining the features

   FileName

   Name of seismic data file (Source: USGS) Character set.

   ImageName

   Name of seismic profile PNG image used as hyperlink (Source: USGS) Character set.

   Shot

   First shot number in seismic profile (Source: USGS) Character set.

   Year

   Calendar year data were collected (Source: USGS) Character set.

   JulDay

   Julian day data were collected. Where Julian day is the integer number representing the interval of time in days since January 1 of the year of collection. (Source: USGS) Character set.

   SurveyID

   WHSC field activity number (Source: USGS) Character set.

   DeviceID

   Sonar device used to collect seismic-reflection data (Source: USGS) Character set.

   VehicleID

   Survey vessel name. (Source: USGS) Character set.

   Shot_end

   Last shot number in seismic profile (Source: USGS)

   Range of values
   Minimum:	1595
   Maximum:	47443

   Length_km

   Length of seismic profile in kilometers (UTM Zone 19N, WGS84) (Source: USGS)

   Range of values
   Minimum:	1.04
   Maximum:	21.02

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • U.S. Geological Survey
2. Who also contributed to the data set?
3. To whom should users address questions about the data?
   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd.

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

Why was the data set created?

How was the data set created?

1. From what previous works were the data drawn?

   Information unavailable from original metadata. (source 1 of 1)

   The source information was incomplete and had to be modified to meet the standard. Assumed to be USGS., unknown, Information unavailable from original metadata..

   Type_of_Source_Media: Information unavailable from original metadata.
   Source_Contribution:

   Seismic-reflection data acquisition 2009-002-FA: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the M/V Megan T. Miller. Chesapeake Technologies' SonarWiz (v.4.04.0031) seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record GPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 100). Data were acquired using a 0.12-s shot rate, a 20-ms pulse length, and a 0.7 to 12 kHz frequency sweep. Traces were recorded in depth, assuming a constant sound velocity of 1500 m/s, with trace lengths of approximately 66 m (1250 samples/trace and .000053-s sample interval). Seismic-reflection data acquisition 2010-004-FA: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the M/V Megan T. Miller. Chesapeake Technologies' SonarWiz (v.4.04.0111) seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record GPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 100). Files l113f1 - l115f1 were acquired using a 0.25-s shot rate, a 5-ms pulse length, and a 0.5 to 8 kHz frequency sweep. Recorded trace lengths were approximately 200 ms (4340 samples/trace and .000046-s sample interval). The remaining files from Julian days 141 - 155 were acquired using a 0.25-s shot rate, a 50-ms pulse length, and a 0.5 to 4.5 kHz frequency sweep. Recorded trace lengths were approximately 199 ms (4328 samples/trace and .000046-s sample interval). Seismic-reflection data acquisition 2011-004-FA: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the M/V Scarlett Isabella of Cape May, NJ. Chesapeake Technologies' SonarWiz (v.5.03.0016) seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record GPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 100). Data were acquired using a 0.25-s shot rate, a 5-ms pulse length, and a 0.5 to 8 kHz frequency sweep. Recorded trace lengths were approximately 200 ms (4340 samples/trace and .000046-s sample interval).

2. How were the data generated, processed, and modified?

   Date: Oct-2011 (process 1 of 9)

   SIOSEIS (version 2010.2.25) was used to read SEG-Y files, renumber shots starting from one, and write out new SEG-Y files. The original shot numbers, which were assigned by SonarWiz sequentially over the duration of an acquisition session despite SEG-Y file changes, are preserved in the raw SEG-Y data. Person who carried out this activity:
   

   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

   Date: Oct-2011 (process 2 of 9)

   Seismic Unix (version 4.2) was used to read renumbered SEG-Y files, write a Seismic Unix file, and extract SEG-Y trace header information, including shot number, longitude, latitude, year, Julian day, and time of day (UTC). Geographic coordinates (WGS84) were converted to UTM zone 19 coordinates (WGS84) using Proj (version 4.6.0). Header information from each SEG-Y file was saved to text files after an AWK (no version) filter was used to maintain the first and last shots, shots at multiples of 100, and shots with unique navigation coordinates. End shots and shots at multiples of 100 may not have unique navigation coordinates. Separate text files containing the first and last shots and even 500 shot intervals were also saved. A 500 shot interval was chosen because it corresponds to the annotation interval provided along the top of the seismic-reflection profile PNG images, which are included in the 2009-002-FA, 2010-004-FA, and 2011-004-FA' folders within 'GIS\hyperlink_images\'. Person who carried out this activity:
   

   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

   Date: Oct-2011 (process 3 of 9)

   An AWK (no version) script was used to apply layback to seismic navigation acquired during portions of the 2010-004-FA and 2011-004-FA surveys when shipboard DGPS was used in lieu of the non-operational GPS receiver mounted on the towed catamaran vehicle. (This includes data collected during Julian days 141 - 155 on 2010-004-FA, and Julian days 134 - 135 (except for 'transit4') on 2011-004-FA. Attributes oldEast and oldNorth in the table 'VS_SeismicShot_unique.csv', which is included in the zip compressed version of the shapefile 'VS_SeismicShot_500.shp', document pre-layback shot/trace positions). The script utilized a read-and-do loop to calculate and apply layback offsets to trace positions. During the initial loop through the script: 1) Easting and northing coordinates (UTM Zone 19, WGS84) for the first five traces of input navigation were read and easting and northing differentials between the consecutive positions were calculated; 2) The signs (+/-) of the differential values were compared to a look-up table to determine the appropriate conversion of the arc tangent (atan2(dy,dx)) angle between consecutive positions to a polar azimuth; 3) The average of the polar azimuths was calculated; 4) The sine and cosine of the average azimuth was calculated and multiplied by the linear distance between the catamaran and the shipboard DGPS receiver (31 or 37 m during 2010-004-FA and 51.5 m during 2011-004-FA), providing absolute values for easting and northing offsets, respectively; 5) A look-up table was used to determine the quadrant of the average azimuth and appropriately add or subtract the calculated offsets to the easting and northing coordinates of the first three input traces, producing final layback positions for those traces; 6) Layback and original easting and northing coordinates for the three adjusted traces were printed to a new layback navigation file that also retained additional attributes input records; and 7) Easting and northing coordinates of the fourth and fifth traces, the three azimuths computed between traces two, three, four, and five, and the average azimuth were held as input for calculations conducted in the subsequent loop. During subsequent loops through the script: 1) Easting and northing coordinates for three additional traces from input navigation were read, and easting and northing differentials were calculated between the consecutive positions, including the last trace position held from the previous loop; 2) Three new polar azimuths were calculated using the differential values, then a new average azimuth was calculated from the three that were held, the new three, and the average held from the previous loop (the previously calculated average was factored into the new average to smooth "kinks" along the layback navigation that can result from significantly different average azimuths calculated from one loop to the next); 3) New layback offset values were computed, and applied to the easting and northing coordinates of the last two traces input during the previous loop, and the first trace input during the present loop. 4) Layback and original easting and northing coordinates for the three adjusted traces were appended to the layback navigation file started in the previous loop; and 5) Easting and northing coordinates of the second and third traces, the three new azimuths, and the average azimuth from the present loop were held as input for calculations conducted in the subsequent loop. Near the end of the input navigation file: 1) If less than three traces were present during a new loop, the layback offsets calculated during the previous loop were applied to remaining trace coordinates; 2) Layback and original easting and northing coordinates for the remaining adjusted traces were appended to the layback navigation file; and 3) The script reached its end, closed, and saved the layback navigation file. In this fashion, the script approximated a moving window, in which the average of six trace to trace azimuths was used to calculate layback offsets for three central trace positions. Exceptions were at the start of a file, where the first three input trace positions were adjusted using offsets calculated from the average of only four azimuths, and possibly at the end of a file, where remaining traces may have been adjusted using the offsets calculated during the previous loop. Person who carried out this activity:
   

   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

   Date: Oct-2011 (process 4 of 9)

   Text files containing unique shot point positions for each seismic line (including the layback-adjusted SB-512i lines from 2010-004-FA and 2011-004-FA) were concatenated into a comma-delimited text file ('VS_SeismicShot_unique.csv', which is provided in the zip-compressed package of the shapefile 'VS_SeismicShot_500.shp'). AWK was used to add and populate attribute fields 'SurveyID', 'DeviceID', and 'VehicleID', then the text file was imported into ArcMap (version 9.3) using 'Add XY data' and saved as points (Geographic, WGS84) in the ESRI shapefile format. Person who carried out this activity:
   

   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

   Date: Oct-2011 (process 5 of 9)

   The shapefile containing unique shot point positions, created in the previous step, was used as an input for VACExtras (version 2.1), a VB collection of tools developed by VeeAnn Cross (USGS-WHSC), which converts point data to a new polyline shapefile ('VS_SeismicTrackline.shp'), based on record order. The 'FileName' field was used to define which points were used to generate each polyline feature, and the fields 'ImageName', 'Shot', 'Year', 'JulDay', 'SurveyID', 'DeviceID', and 'Shot_end' were chosen to be included as attributes in the output shapefile. Using XTools Pro (version 7.1.0) for ArcGIS desktop, the length of each polyline segment was calculated and included in the attribute field 'Length_km', specifying UTM, Zone 19 N, WGS84, and kilometers. Person who carried out this activity:
   

   Wayne Baldwin

   U.S. Geological Survey

   Geologist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   508-457-2310 (FAX)

   wbaldwin@usgs.gov

   Date: 27-May-2016 (process 6 of 9)

   Edits to the metadata were made to fix any errors that MP v 2.9.32 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). Fixed a link to the project page in the abstract. Fixed a link in the cross-reference section to the SEG-Y format documentation. The source information was incomplete and had to be modified to meet the standard. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Rd.

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

   Date: 20-Jul-2018 (process 7 of 9)

   USGS Thesaurus keywords added to the keyword section. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Road

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

   Date: 18-Nov-2019 (process 8 of 9)

   Crossref DOI link was added as the first link in the metadata. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Road

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

   Date: 08-Sep-2020 (process 9 of 9)

   Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Road

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

3. What similar or related data should the user be aware of?
   Stockwell, John, 2011, CWP/SU: Seismic Unix: Center for Wave Phenomena - Colorado School of Mines, Golden, CO.

   Online Links:

   • http://www.cwp.mines.edu/cwpcodes/index.html

   Henkart, Paul, 2011, SIOSEIS: Scripps Institution of Oceanography, University of California - San Diego, LaJolla, CA.

   Online Links:

   • http://sioseis.ucsd.edu/index.html

   Michael W. Norris and Alan K. Faichney, 2002, SEGY Rev.1 Data Exchange Format1: Society of Exploration Geophysicists, Tulsa, OK.

   Online Links:

   • http://www.seg.org/

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?
   All attributes were checked in a consistent manner.
2. How accurate are the geographic locations?
   Field activity 2009-002-FA: The SB-0512i was mounted on a catamaran sled and towed at the sea surface approximately 30 - 40 m astern of the M/V Megan T. Miller. Position data were provided by a Global Positioning System (GPS) navigation receiver mounted on the catamaran, and data were transmitted to the acquisition computer on the vessel via a 2.4 GHz radio link. Positional accuracy is assumed to be ±10 m. Field activity 2010-004-FA: The SB-0512i was mounted on a catamaran sled and towed at the sea surface approximately 30 - 40 m astern of the M/V Megan T. Miller. DGPS navigation was obtained from a receiver mounted on top of the acquisition van. Layback positions, which account for the linear distance between the shipboard DGPS receiver and the towed catamaran vehicle, were calculated trigonometrically during post-processing (see processing step 3). Positional accuracy is assumed to be ±20 m; increased uncertainty arises because layback calculations do not account for fish motion behind the vessel, which is caused by sea state and vessel speed induced changes in the angle and scope of the tow cable. Field activity 2011-004-FA: The SB-0512i was mounted on a catamaran sled and towed at the sea surface approximately 50 m astern of the M/V Scarlett Isabella. Position data were provided by a Global Positioning System (GPS) navigation receiver mounted on the catamaran, and data were transmitted to the acquisition computer on the vessel via a 2.4 GHz radio link. Technical difficulties during portions of 2011-004-FA caused the GPS system mounted on the catamaran to malfunction, so DGPS navigation was obtained from a receiver mounted above the interferometric sonar head (This applies to all files acquired over Julian days 134-137). Layback positions, which account for the linear distance between the shipboard DGPS receiver and the towed catamaran vehicle, were calculated trigonometrically during post-processing (see processing step 3). While the vehicle mounted GPS antenna was operational, positional accuracy is assumed to be ±10 m. While the vehicle mounted GPS was not operational, positional accuracy is assumed to be ±20 m; increased uncertainty arises because layback calculations do not account for fish motion behind the vessel, which is caused by sea state and vessel speed induced changes in the angle and scope of the tow cable.
3. How accurate are the heights or depths?
   
4. Where are the gaps in the data? What is missing?
   Sections of tracklines where navigation was recorded but no seismic data were logged are not included. Only the subsets of seismic-reflection data collected during field activities 2009-002-FA, 2010-004-FA, and 2011-004-FA that are within the Vineyard Sound study are included in this spatial dataset. Trackline navigation for approximately 4500 km of additional seismic-reflection profiles collected within Buzzards Bay, Massachusetts during these field activities were published in USGS Open-File Report 2012-1002 High-Resolution Geophysical Data from the Inner Continental Shelf: Buzzards Bay, Massachusetts (http://pubs.usgs.gov/of/2012/1002/).
5. How consistent are the relationships among the observations, including topology?
   Any spurious data points were removed during processing. For each seismic trackline there is one seismic-profile image that is hyperlinked by the field 'IMAGENAME'. No duplicates exist.

How can someone get a copy of the data set?

1. Who distributes the data set? (Distributor 1 of 1)
   
   Wayne Baldwin

   U.S. Geological Survey, Woods Hole Science Center

   Geologist

   384 Woods Hole Rd.

   Woods Hole, MA
   

   USA

   508-548-8700 x2226 (voice)

   wbaldwin@usgs.gov
2. What's the catalog number I need to order this data set? Downloadable Data
3. What legal disclaimers am I supposed to read?
   Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
4. How can I download or order the data?
   • Availability in digital form:

     Data format:	Trackline navigation for EdgeTech SB-512i chirp seismic-reflection data collected by the U.S. Geological Survey offshore of Massachusetts within Vineyard Sound and associated metadata. in format SHP (version ArcGIS 9.3) ESRI polyline shapefile Size: 14.2
     Network links:	http://pubs.usgs.gov/of/2012/1006/GIS/shapefile/VS_SeismicTrackline.zip
     Media you can order:	DVD-ROM (Density 4.75 Gbytes) (format UDF)

   • Cost to order the data: none

5. What hardware or software do I need in order to use the data set?
   This zip file contains data available in Environmental Systems Research Institute (ESRI) shapefile format. The user must have software capable of uncompressing the WinZip file and displaying the shapefile. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing the data. A free data viewer, ArcExplorer, capable of displaying the data is available from ESRI at www.esri.com.

Who wrote the metadata?

Dates:

Last modified: 18-Mar-2024

Metadata author:

Wayne Baldwin

U.S. Geological Survey

Geologist

384 Woods Hole Rd.

Woods Hole, MA

USA

508-548-8700 x2226 (voice)

508-457-2310 (FAX)

whsc_data_contact@usgs.gov

Contact_Instructions:

The metadata contact email address is a generic address in the event the person is no longer with USGS. (updated on 20240318)

Metadata standard:

FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)