Offline Field Surveys with MariField

Marine monitoring often happens in places where internet connectivity is unreliable or nonexistent: remote islands, offshore reefs, mangrove channels, and boat-based operations far from cell towers. MariField is built for exactly these conditions. The app works fully offline, storing all survey data locally on the device and syncing to MariMap when connectivity returns. No internet connection is needed during data collection.

At a glance

• MariField works fully offline during field data collection.
• Sync survey protocols, species lists, and site data before going to the field.
• GPS coordinates and depth metadata are captured automatically during surveys.
• Photos and videos attach to observation units for QA/QC.
• Data syncs to MariMap when connectivity returns, with validation and conflict resolution.
• Designed for remote deployments: island sites, boat-based surveys, and areas with no cell coverage.

How MariField works offline

MariField uses a local SQLite database on the device to store all survey data. When the app has internet access, it syncs with MariMap in both directions:

• Download (MariMap to MariField): survey plans, protocols, species lists, site boundaries, team assignments, and any previously collected data.
• Upload (MariField to MariMap): completed observations, photos, GPS tracks, and survey status updates.

Between sync events, all data entry happens against the local database. The app does not require a network connection to create observations, navigate between survey units, or attach photos.

Sync states

Each survey in MariField has a sync status:

Preparing before going to the field

Good preparation is the single most important factor for successful offline fieldwork. Do these steps while you still have connectivity:

1) Sync survey plans and protocols

1. Open MariField and connect to your MariMap account.
2. Navigate to the project and site you will be surveying.
3. Pull the latest survey plans, including transect geometry and quadrat locations.
4. Confirm that all assigned surveys appear in your survey list.

2) Download species and category lists

1. In MariField settings, check the offline data section.
2. Download the benthic category list, fish taxonomy list, and seagrass species list as needed.
3. Verify that the lists contain the species relevant to your region.

These lists are essential for data entry. Without them, you will not be able to select species or substrate categories during the survey.

3) Verify team assignments

1. Confirm which surveys and transects are assigned to each team member.
2. Each diver should see their assigned units in MariField before departing.
3. Set up any shared devices with the correct user account and survey access.

4) Check device readiness

• Storage: confirm sufficient space for photos and data (see battery and storage management below).
• Battery: charge the device fully. Bring external battery packs for multi-day trips.
• GPS: test that the device can acquire a GPS fix. Enable location services.
• Waterproof housing: if using the device underwater, test the housing seal before the trip.

Collecting data underwater without internet

During the dive or snorkel survey:

1. Open the assigned survey in MariField. All protocols, geometry, and category lists are available from the local database.
2. Navigate to the first observation unit (transect, quadrat, or photo point).
3. Enter observations using the standard data entry interface. The workflow is identical to online data entry.
4. GPS coordinates are captured automatically when the observation is recorded. For underwater surveys, the GPS fix is taken at the surface before descent or interpolated from the dive track.
5. Depth metadata can be entered manually or captured from a connected dive computer if supported.
6. Move to the next unit and repeat until the survey is complete.

The app saves data continuously to the local database. There is no "save" button to forget. If the app closes unexpectedly (battery, crash, housing leak), all data recorded up to that point is preserved.

GPS tagging and depth metadata

GPS tagging

MariField captures GPS coordinates at several levels:

• Survey level: the general location when the survey was started.
• Observation unit level: coordinates for each transect start point, quadrat center, or photo point.
• Individual observation level: optional GPS stamps for specific records.

For underwater surveys, GPS coordinates are typically captured at the surface before descent. If the device is in a waterproof housing at the surface, it can acquire a fix before the diver descends. For deep dives, the survey-level GPS plus depth metadata provide the spatial reference.

Depth metadata

Depth can be recorded in three ways:

1. Manual entry: the diver enters the depth in meters for each transect or quadrat.
2. Dive computer integration: where supported, depth is logged from a connected Bluetooth dive computer.
3. Survey plan default: if the plan specifies a depth range for the site, that value is pre-filled.

Photo and video capture during surveys

Photos and videos are attached to observation units for documentation, QA/QC, and later analysis:

1. In the observation unit, tap the camera icon to capture a photo or video.
2. Frame the subject: for quadrats, shoot from directly above; for transects, capture representative sections.
3. Photos are stored locally on the device alongside the observation data.
4. File naming is automatic: MariField labels each photo with the survey ID, unit ID, and timestamp.
5. Review photos after the dive to confirm quality before leaving the site.

Storage note: photos and videos consume significantly more storage than observation data. A single survey campaign with hundreds of photos can use several gigabytes. See the storage management section below.

What happens when connectivity returns

When MariField detects an internet connection (Wi-Fi or cellular):

1. Pending uploads appear in the sync queue.
2. The app uploads observation data first, then photos and videos (larger files sync after the critical data).
3. Validation runs during upload: MariMap checks for required fields, valid species codes, and geometry consistency.
4. If validation passes, the survey status moves to SYNCED.
5. If validation fails, the app flags specific issues for the user to correct before re-syncing.

You can also trigger sync manually from the sync screen if you want to control timing (e.g., sync over Wi-Fi only, not cellular).

Conflict resolution

Conflicts occur when the same survey or observation has been edited in both MariField (offline) and MariMap (by another team member online). This is uncommon but can happen in team scenarios.

When a conflict is detected:

1. MariField shows the CONFLICT status on the affected survey.
2. Opening the survey displays both versions: the local version and the server version.
3. The user chooses which version to keep, or merges specific fields from each.
4. After resolution, the merged data syncs to MariMap.

Prevention tips:

• Assign each transect or quadrat to a single diver to avoid overlapping edits.
• Sync all devices before and after each field day.
• Use the survey plan assignments to prevent two people from editing the same unit.

Tips for remote field sites

Island deployments

• Sync all data before departing the mainland.
• Bring a portable Wi-Fi hotspot or satellite communicator for emergency sync if available.
• Plan for multi-day offline periods. MariField handles weeks of offline use without issues.
• Charge devices from solar panels or generator power. Bring adapters for local power configurations.

Boat-based surveys

• Sync at the dock or marina before departure.
• Assign surveys and transects to specific devices before leaving port.
• Store devices in dry bags between dives.
• Review data on the boat after each dive to catch errors while memories are fresh.
• Sync at the end of each day if the vessel has satellite or cellular coverage.

Multi-device teams

• Each device should be logged into a separate MariMap user account.
• Assign non-overlapping survey units to each device.
• Designate one device as the "sync lead" that uploads first, resolving any potential conflicts.
• Brief the team on the sync workflow before the first day of fieldwork.

Battery and storage management

Battery

• MariField uses GPS and screen brightness as the primary battery consumers.
• Reduce screen brightness to 50% or lower during data entry.
• Close other apps running in the background.
• Enable airplane mode during underwater surveys to save battery (GPS still works in airplane mode on most devices).
• A fully charged modern smartphone typically supports 6-8 hours of active MariField use.
• Carry external battery packs rated at least 10,000 mAh for multi-dive days.

Storage

• Observation data (text records) is minimal: thousands of records use less than 50 MB.
• Photos are the main storage consumer: approximately 3-5 MB per photo, 20-50 MB per video.
• A 100-quadrat survey with photos can use 500 MB to 1 GB.
• Before a campaign, clear unnecessary files from the device and confirm at least 5 GB of available storage.
• Consider reducing photo resolution in MariField settings if storage is tight.

MRV readiness and disclosure alignment

• Baseline vs repeat surveys: mark baselines and keep repeat surveys on comparable geometry.
• Monitoring plan logic: define cadence, QA/QC thresholds, and conservative handling of uncertainty.
• Outcome types and claims discipline: record uplift, avoided loss, or maintenance credits; separate inputs from verified outcomes.
• Rights and integrity: document FPIC, customary marine tenure, OECM, ICCA, benefit sharing, durability mechanisms, and leakage risk.
• Disclosure alignment: map indicators to TNFD, CSRD, ESRS, EU Taxonomy, SBTN, and SBTi requirements.
• Use the Metrics Reference and Data Providers for definitions and sources.

Related guides

• Planning Surveys and Data Collection
• Benthic Transect Methods: PIT and LIT
• Fish Belt Transect Surveys in MariMap
• Team Collaboration and Access Management

References

• Reef Support Platform