Metadata: Identification_Information: Citation: Citation_Information: Originator: U.S. Geological Survey Publication_Date: 2018 Title: Multibeam Echosounder, Reson T-20P deep site backscatter (4-m), USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (8-bit GeoTIFF, UTM Zone 16N, NAD 83) Edition: 1.0 Geospatial_Data_Presentation_Form: remote-sensing image Series_Information: Series_Name: data release Issue_Identification: DOI:10.5066/F7X929K6 Publication_Information: Publication_Place: Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts Publisher: U.S. Geological Survey, Coastal and Marine Geology Program Online_Linkage: https://doi.org/10.5066/F7X929K6 Online_Linkage: https://www.sciencebase.gov/catalog/item/5a945127e4b069906068fa04 Larger_Work_Citation: Citation_Information: Originator: Wayne E. Baldwin Originator: Seth D. Ackerman Originator: Charles R. Worley Originator: William W. Danforth Originator: Jason D. Chaytor Publication_Date: 2018 Title: High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA Edition: 1.0 Series_Information: Series_Name: data release Issue_Identification: DOI:10.5066/F7X929K6 Publication_Information: Publication_Place: Reston, VA Publisher: U.S. Geological Survey Other_Citation_Details: Suggested citation: Baldwin, W.E., Ackerman, S.D., Worley, C.R., Danforth, W.W., and Chaytor, J.D, 2018, High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA: U.S. Geological Survey data release, https://doi.org/10.5066/F7X929K6. Online_Linkage: https://doi.org/10.5066/F7X929K6 Online_Linkage: https://www.sciencebase.gov/catalog/item/5a8c4bcbe4b00f54eb44044c Description: Abstract: High resolution bathymetric, sea-floor backscatter, and seismic-reflection data were collected offshore of southeastern Louisiana aboard the research vessel Point Sur on May 19-26, 2017, in an effort to characterize mudflow hazards on the Mississippi River Delta front. As the initial field program of a research cooperative between the U.S. Geological Survey, the Bureau of Ocean Energy Management, and other Federal and academic partners, the primary objective of this cruise was to assess the suitability of sea-floor mapping and shallow subsurface imaging tools in the challenging environmental conditions found across delta fronts (for example, variably distributed water column stratification and widespread biogenic gas in the shallow subsurface). Approximately 675 kilometers (km) of multibeam bathymetry and backscatter data, 420 km of towed chirp data, and 550 km of multichannel seismic data were collected. Varied mudflow (gully, lobe), prodelta morphologies, and structural features were imaged in selected survey areas from Pass a Loutre to Southwest Pass. Purpose: This 4-m per pixel image represents the processed dual Reson T20P multibeam echosounder time-series backscatter data collected at a deep water site on the southern Mississippi River Delta front, where large mudflow lobes are known to intersect the trends of pipeline infrastructure on the sea floor. The site was also chosen to test performance of the T20P configuration in water depths between 100 and 300 meters. The image is intended to be used in conjunction with other geophysical and sample data to investigate sea-floor morphology and geologic framework of mudflow features in the area. Supplemental_Information: Additional information on the field activity is available from https://cmgds.marine.usgs.gov/fan_info.php?fan=2017-003-FA. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 20170524 Ending_Date: 20170525 Currentness_Reference: ground condition Status: Progress: Complete Maintenance_and_Update_Frequency: None planned. Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -89.139399 East_Bounding_Coordinate: -89.026246 North_Bounding_Coordinate: 28.884907 South_Bounding_Coordinate: 28.798288 Keywords: Theme: Theme_Keyword_Thesaurus: USGS Metadata Identifier Theme_Keyword: USGS:5a945127e4b069906068fa04 Theme: Theme_Keyword_Thesaurus: None Theme_Keyword: U.S. Geological Survey Theme_Keyword: USGS Theme_Keyword: Woods Hole Coastal and Marine Science Center Theme_Keyword: WHCMSC Theme_Keyword: Coastal and Marine Geology Program Theme_Keyword: CMGP Theme_Keyword: Bureau of Ocean Energy Management Theme_Keyword: BOEM Theme_Keyword: field activity number 2017-003-FA Theme_Keyword: GeoTIFF Theme_Keyword: multibeam echosounder Theme_Keyword: multibeam bathymetry Theme_Keyword: multibeam backscatter Theme_Keyword: Reson Theme_Keyword: T20P Theme_Keyword: bathymetry Theme_Keyword: backscatter Theme_Keyword: Marine Geology Theme: Theme_Keyword_Thesaurus: ISO 19115 Topic Category Theme_Keyword: oceans Theme_Keyword: geoscientificInformation Theme_Keyword: imageryBaseMapsEarthCover Theme: Theme_Keyword_Thesaurus: USGS Thesaurus Theme_Keyword: multibeam sonar Theme_Keyword: sea-floor acoustic reflectivity Theme_Keyword: bathymetry Theme_Keyword: marine geophysics Theme_Keyword: marine geology Place: Place_Keyword_Thesaurus: None Place_Keyword: Gulf of Mexico Place_Keyword: Mississippi River Delta front Place_Keyword: Southwest Pass Place_Keyword: South Pass Place_Keyword: Southeast Louisiana Place_Keyword: Pass a Loutre Stratum: Stratum_Keyword_Thesaurus: None Stratum_Keyword: sea floor Stratum_Keyword: seafloor Temporal: Temporal_Keyword_Thesaurus: none Temporal_Keyword: 2017 Access_Constraints: none Use_Constraints: Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset. Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Person: Wayne E. Baldwin Contact_Position: Geologist Contact_Address: Address_Type: mailing and physical Address: 384 Woods Hole Road City: Woods Hole State_or_Province: Massachusetts Postal_Code: 02543-1598 Country: US Contact_Voice_Telephone: 508-548-8700 x2226 Contact_Facsimile_Telephone: 508-457-2310 Contact_Electronic_Mail_Address: wbaldwin@usgs.gov Browse_Graphic: Browse_Graphic_File_Name: https://www.sciencebase.gov/catalog/file/get/5a945127e4b069906068fa04/?name=2017-003-FA_T20P_Backscatter_deepsite_browse.jpg Browse_Graphic_File_Description: Thumbnail image of 4-m multibeam echosounder backscatter data collected within a deep water site on the Mississippi River Delta front, southeastern Louisiana. Browse_Graphic_File_Type: JPEG Data_Quality_Information: Logical_Consistency_Report: This image represents processed dual Reson T20P multibeam echosounder (MBES) backscatter data mosaicked at 4-m resolution. Quality control and data processing were conducted to remove spurious points and reduce sound speed artifacts (refraction) using Computer Aided Resource Information System (Caris) Hydrographic Information Processing System (HIPS; versions 10.2 and 10.4). Despite processing, noticeable vessel motion and refraction artifacts remain in the data, particularly in the area surveyed adjacent to Southwest Pass (see GeoTiff 2017-003-FA_Bathy_swpasssite.tif available from the larger work citation). Several factors contributed to difficulty during acquisition and processing. As the initial deployment of the dual system configuration on a vessel of opportunity, considerable testing and troubleshooting was expected. Environmental conditions were also challenging over the five day cruise, including several periods of inclement weather with high winds and waves and the Mississippi River in flood stage, a combination of factors that certainly contributed to the residual artifacts present in the data. While the navigation and attitude data in the backscatter and bathymetry data are identical, the extents of the processed bathymetry grid and backscatter mosaic differ slightly due to differences in processing of the HYPACK HSX bathymetry and SeaBat User Interface s7k backscatter data. Completeness_Report: Most T20P MBES backscatter data collected at the deep water site were used to produce this grid. This includes the time periods: 03:08 (UTC) - 08:08 and 08:30 - 17:29 5/24/2017 (JD144), and 00:46 - 06:52 and 07:21 - 15:59 5/25/2017 (JD145). Omissions consisted of data collected during transits, dip lines (lines run generally perpendicular to the delta shoreline, occupied primarily for seismic-reflection acquisition), turns, and one line collected seaward of the contiguous survey area. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Navigation data were acquired using the WGS 84 coordinate system with an Applanix POS MV Wavemaster (model 220, V5), which blends Global Navigation Satellite Systems (GNSS) with acceleration data from a Motion Reference Unit (MRU) and GPS azimuthal heading. The POS MV was configured with two AeroAntenna Technologies GPS antennas located at either end of a 2-m baseline, which was oriented fore and aft and mounted atop the MBES pole, approximately amidships on the starboard side of vessel. DGPS positions were obtained from the primary antenna located on the forward end of the baseline, and the positional offsets between the antenna and the navigational reference point (the POS MV IMU) were accounted for in the Applanix POSView (version 8.60) acquisition software. DGPS positions are horizontally accurate to 0.5 - 2 meters, but accuracy can increase to less than 10 cm after post-processing with Applanix POSPac (version 8.1). Lineage: Source_Information: Source_Citation: Citation_Information: Originator: U.S. Geological Survey Publication_Date: Unpublished Material Title: raw MBES data in s7k format Geospatial_Data_Presentation_Form: raster digital data Type_of_Source_Media: disc Source_Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 20170524 Ending_Date: 20170525 Source_Currentness_Reference: ground condition Source_Citation_Abbreviation: Reson T20P multibeam echosounder raw bathymetry and backscatter Source_Contribution: Multibeam echosounder bathymetry, backscatter, and water column data were collected using dual Reson T20P MBES. The pair of Mills Cross transmit and receive arrays were placed side-by-side within a bracket that oriented them at opposing 30 degree angles (relative to horizontal). The bracket was pole-mounted on the starboard side of the R/V Point Sur so that the sonar arrays were oriented athwart ships (primary and secondary arrays facing outward and down to port and starboard, respectively) and located approximately 3.04 m below the waterline when deployed. Vessel navigation and attitude data were acquired with an Applanix POS MV Wavemaster (model 220, V5) configured with two AeroAntenna Technologies GPS antennas located at either end of a 2-m baseline, which was oriented fore and aft and mounted atop the MBES pole approximately amidships on the starboard side of vessel, and the wet pod MRU mounted atop the sonar bracket just aft of the pole. An AML Micro X SV mounted on the sonar bracket monitored sound speed near the sonars during acquisition, and an ODIM MVP30 moving vessel profiler (MVP), mounted on the stern, was used to collect water column sound speed profiles at 1 to 5 hour intervals while underway (See shapefile 2017-003-FA_MVPdata.shp available from the larger work citation). The Reson SeaBat User Interface (version 5.0.0.6) was used to control the sonars, which were operated in intermediate mode at full power (220 db), with frequency modulated pulses between 200 to 300 kHz. The range of the 1024 across track beams formed by the sonars were adjusted manually depending on water depth, and resulted in combined swath widths of 60 to 500 meters or typically 3 to 6 times the water depth. Data were monitored and recorded using the Reson SeaBat User Interface (version 5.0.0.6) and HYPACK/HYSWEEP (version 2017, 17.1.3.0). The SeaBat User Interface logged the navigation, attitude, bathymetry, time-series backscatter, and water column data to s7k format files for each sonar. HYSWEEP logged the navigation, attitude, and bathymetry data for both sonars to a single HSX format file, the time series backscatter data for both sonars to a single 7k format file, and water column data to 7k format files for each sonar. HYPACK HSX data were used to produce the final processed bathymetry grids, and Reson SeaBat User Interface s7k data were used to produce the final processed backscatter mosaics. Process_Step: Process_Description: Shipboard multibeam data processing within Caris HIPS (version 10.2) consisted of the following flow: 1) A Caris HIPS project (version 10.2) was created with projection information set to Universal Transverse Mercator (UTM) Zone 16N, WGS 84. 2) A vessel configuration file was created in Caris for the R/V Point Sur, which included relevant linear and angular installation offsets for each T20P unit as well as vendor specified uncertainty values for each of the survey sensors. 3) Each SeaBat User Interface s7k file was imported to the new Caris project using the Import/Conversion Wizard. 4) Delayed heave data from raw POS MV files were used to update HIPS survey lines using the import auxiliary data function. 5) Navigation was reviewed and edited as needed using the Navigation Editor tool. 6) Sound velocity correction was applied using the Caris algorithm, a master SVP file containing all the sound velocity profiles collected during the cruise and specifying the nearest in distance method, delayed heave source, and use surface sound speed. 7) Data were merged selecting no tide and the delayed heave source. 8) 5-m resolution Bathymetry Associated with Statistical Error (BASE) surfaces were created to incorporate files for each Julian day as they were processed, and the BASE surfaces were reviewed for inconsistencies and anomalies. 9) The swath and subset editors were used to remove spurious points through manual editing and filter application, and the refraction editor was used to adjust sound speed values in areas where velocimeter data did not adequately correct depth profiles obviously influenced by local anomalies in speed of sound through the water column. 10) Survey lines adjusted for refraction anomalies were remerged, and the respective BASE surfaces were recomputed to reflect the changes. Shipboard processing was primarily focused on QA/QC during acquisition. Editing processes did require trial and error, and were at times iterative. This process step and all subsequent process steps were conducted by the same person - Wayne Baldwin. Process_Date: 201705 Process_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Person: Wayne Baldwin Contact_Position: Geologist Contact_Address: Address_Type: mailing and physical address Address: 384 Woods Hole Rd. City: Woods Hole State_or_Province: MA Postal_Code: 02543-1598 Contact_Voice_Telephone: 508-548-8700 x2226 Contact_Facsimile_Telephone: 508-457-2310 Contact_Electronic_Mail_Address: wbaldwin@usgs.gov Process_Step: Process_Description: Post-cruise processing within Caris HIPS (version 10.4) consisted of the following flow: 1) Post-processed navigation, vessel attitude, and GPS height data from POSPac SBET files, and post-processed rms attitude error data from POSPac smrmsg files were used to update HIPS survey lines using the import auxiliary data function. 2) All lines were updated with Applanix SBET set as the navigation source, and navigation was reviewed and edited as needed using the Navigation Editor tool. 3) Sound velocity correction was reapplied using the Caris algorithm, the master SVP file containing all the sound velocity profiles collected during the cruise and specifying the nearest in distance method, delayed heave source, and use surface sound speed. 4) Data were remerged selecting no tide and the delayed heave source. 5) Total Propagated Uncertainty (TPU) was computed specifying POSPac smrmsg and delayed heave values. 6) A 4-m resolution Combined Uncertainty Bathymetry Estimator (CUBE) surface was created with all files incorporated in the deep water survey area, using IHO S-44 Order, Special Order specifications, with a Density and Locale Disambiguation method as a CUBE parameter. 7) Additional editing was conducted using the swath and subset editors to minimize inconsistencies and artifacts, and the CUBE surface was recomputed to reflect the changes. Process_Date: 201712 Process_Step: Process_Description: Processing within QPS FlederMaus Geocoder Tool (FMGT, version 7.7.5) consisted of the following flow: 1) Create a project and set project coordinate system to UTM zone 16 N NAD 83, so that the mosaic product will match the coordinate system of the equivalent bathymetric grid (see 2017-003-FA_T20P_Bathy_deepsite.tif available from the larger work citation). 2) Set all import parameters for the Reson T20P (Edit - Processing Parameters). Defaults were accepted except for: Adjust tab, uncalibrated backscatter range of 85 decibels (db) 125 db and Head 1 bias of -4; Filter tab, apply flat angle varying gain with a window of 300; Sonar Defaults tab, custom override all checked, Reson SeaBat T20P Focused MBES sonar type, primary frequency 200 kHz, no head 1 db reference value, and apply edits. 3) Import raw data as "Source/Paired Files". The source pairs consist of the Reson SeaBat User Interface s7k files, which contain the raw datagrams (bathymetry, attitude, time-series backscatter, navigation) needed for backscatter processing, and Caris HIPS files, which contain processed bathymetric solutions that FMGT uses to correct for slope and depth. WGS 84 navigation in the s7k headers are transformed to NAD 83 during the import process. 4) Set mosaic size to 4-m per pixel and mosaic data, creating an output Fledermaus SD (scientific data) file. 5) Use backscatter adjust function to adjust bias of individual line files to improve tonal balance of overall mosaic, and manually adjust histogram to encompass the range 92 db 100 db. 6) Export mosaic to an 8-bit greyscale GeoTIFF image (UTM Zone 16N, NAD 83). Process_Date: 201801 Process_Step: Process_Description: Create final single band 8-bit greyscale GeoTIFF and define spatial reference information: GeoTiffExamine (no version) was used to read the exported GeoTIFF file and write an external world file (tfw) containing georeferencing information extracted from the GeoTIFF header. Adobe Photoshop CS6 (version 13.0) was used to flatten the two band raster, and save a single band image with a white background (8-bit value 255). The flattened image was imported into Global Mapper (version 17.1) and exported as the GeoTIFF '2007-003-FA_T20P_Backscatter_deepsite.tif' in order to repopulate the GeoTIFF header with the georeferencing information. Process_Date: 201801 Process_Step: Process_Description: Added keywords section with USGS persistent identifier as theme keyword. Process_Date: 20200807 Process_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Person: VeeAnn A. Cross Contact_Position: Marine Geologist Contact_Address: Address_Type: Mailing and Physical Address: 384 Woods Hole Road City: Woods Hole State_or_Province: MA Postal_Code: 02543-1598 Contact_Voice_Telephone: 508-548-8700 x2251 Contact_Facsimile_Telephone: 508-457-2310 Contact_Electronic_Mail_Address: vatnipp@usgs.gov Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Raster Raster_Object_Information: Raster_Object_Type: Pixel Row_Count: 2303 Column_Count: 2692 Vertical_Count: 1 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Grid_Coordinate_System: Grid_Coordinate_System_Name: Universal Transverse Mercator Universal_Transverse_Mercator: UTM_Zone_Number: 16N Transverse_Mercator: Scale_Factor_at_Central_Meridian: 0.9996 Longitude_of_Central_Meridian: -87 Latitude_of_Projection_Origin: 0 False_Easting: 500000 False_Northing: 0 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: row and column Coordinate_Representation: Abscissa_Resolution: 4.0 Ordinate_Resolution: 4.0 Planar_Distance_Units: meters Geodetic_Model: Horizontal_Datum_Name: D_North_American_1983 Ellipsoid_Name: GRS_1980 Semi-major_Axis: 6378137.000000 Denominator_of_Flattening_Ratio: 298.257222 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: Image pixel values contain acoustic reflectivity values normalized to an 8-bit data range. Low-backscatter is represented by dark tones (low values) and high-backscatter is represented by bright tones (high values). The background color is set to 255 and can be turned off without removing data values. Entity_and_Attribute_Detail_Citation: U.S. Geological Survey Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey - ScienceBase Contact_Address: Address_Type: mailing and physical address Address: Federal Center Address: Building 810 Address: Mail Stop 302 City: Denver State_or_Province: CO Postal_Code: 80225 Contact_Voice_Telephone: 1-888-275-8747 Resource_Description: USGS data release 2017-003-FA multibeam echosounder 4-m backscatter at a deep water site in the Mississippi River Delta front area: includes the GeoTIFF image 2017-003-FA_T20P_Backscatter_deepsite.tif, the browse graphic 2017-003-FA_T20P_Backscatter_deepsite_browse.jpg, and the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (CSDGM) metadata file 2017-003-FA_T20P_Backscatter_deepsite_meta.xml. Distribution_Liability: 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. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: GeoTIFF Format_Version_Number: Global Mapper (version 17.1.0) Format_Specification: 8-bit GeoTIFF image Format_Information_Content: GeoTIFF image derived from MBES time-series backscatter data collected by the U.S. Geological Survey - Woods Hole Coastal and Marine Science Center along the Mississippi River Delta front and the associated metadata. File_Decompression_Technique: none Transfer_Size: 5.9 Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://www.sciencebase.gov/catalog/item/5a945127e4b069906068fa04 Network_Resource_Name: https://www.sciencebase.gov/catalog/file/get/5a945127e4b069906068fa04 Network_Resource_Name: https://doi.org/10.5066/F7X929K6 Access_Instructions: The first link is to the page containing the data, the second link downloads all data available from the page as a zip file, and the third link is to the publication landing page. Digital_Form: Digital_Transfer_Information: Format_Name: WCS Format_Information_Content: 8-bit GeoTIFF 2017-003-FA_T20P_Backscatter_deepsite.tif provided through a WCS (web coverage service). Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://www.sciencebase.gov/catalogMaps/mapping/ows/5a945127e4b069906068fa04?service=wcs&request=getcapabilities&version=1.0.0 Network_Resource_Name: https://www.sciencebase.gov/catalog/item/5a945127e4b069906068fa04 Network_Resource_Name: https://doi.org/10.5066/F7X929K6 Access_Instructions: The first link in the network resources accesses the data through a coverage service, the second is to the page containing the data, and the third link is to the publication landing page. Digital_Form: Digital_Transfer_Information: Format_Name: WMS Format_Information_Content: 8-bit GeoTIFF 2017-003-FA_T20P_Backscatter_deepsite.tif provided through a WMS (web mapping service). Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://www.sciencebase.gov/catalogMaps/mapping/ows/5a945127e4b069906068fa04?service=wms&request=getcapabilities&version=1.3.0 Network_Resource_Name: https://www.sciencebase.gov/catalog/item/5a945127e4b069906068fa04 Network_Resource_Name: https://doi.org/10.5066/F7X929K6 Access_Instructions: The first link in the network resources accesses the data through a mapping service, the second is to the page containing the data, and the third link is to the publication landing page. Fees: none Technical_Prerequisites: To utilize these data, the user must have software capable of viewing GeoTIFF files, or GIS software capable of utilizing web mapping or coverage services. Metadata_Reference_Information: Metadata_Date: 20200807 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Person: Wayne E. Baldwin Contact_Position: Geologist Contact_Address: Address_Type: mailing and physical Address: 384 Woods Hole Rd. City: Woods Hole State_or_Province: MA Postal_Code: 02543-1598 Contact_Voice_Telephone: (508) 548-8700 x2226 Contact_Facsimile_Telephone: (508) 457-2310 Contact_Electronic_Mail_Address: wbaldwin@usgs.gov Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998 Metadata_Time_Convention: local time