The National Oceanic Atmospheric Administration (NGS) Continuously Operating Reference Stations (CORS) Network (NCN), managed by NOAA/National Geodetic Survey, provide Global Navigation Satellite System (GNSS) data, supporting three-dimensional positioning, and geophysical applications throughout the United States.  The CORS network is a multi-purpose, multi-agency cooperative endeavor.  Surveyors, GIS users, engineers, scientists, and other people who collect GPS/GNSS data can use NCN data to align their work within the National Spatial Reference System (NSRS). NCN enhanced post-processed coordinate accuracies can approach a few centimeters, both horizontally and vertically.

ADWR manages and operates the Arizona CORS Network (AZCORS). AZCORS consisted of 23 - State-owned CORS sites, 4 – cooperator-owned CORS sites managed by other Agencies, and 15 - CORS sites operated by other CORS Networks in Arizona (EarthScope and the National Park Service), for a total of 42 CORS sites. ADWR operates and maintains two virtual servers and software to operate the AZCORS network and distribute the data to other Federal, State, County, and Local agencies, commercial and private entities, and the public.  Each CORS station consists of a mounting pole, a GPS receiver, a GPS antenna, a cellular router, and associated electronics.

The CORS sites provide high-precision survey data and is the backbone of the geodetic network for Arizona that is used by Federal, State, County, and Local agencies, commercial and private entities, and the public. This data is used for any type of program, project, and/or application that requires accurate horizontal and vertical data such as surveying, mapping, infrastructure, and emergency response projects.  

How to register for AZCORS, network map, and list of mountpoints. 

AZCORS site

What is InSAR

Synthetic Aperture Radar (SAR) is a side-looking, active (produces its own illumination), radar imaging system that transmits a pulsed microwave signal towards the earth and records both the amplitude and phase of the back-scattered signal that returns to the antenna. Interferometric SAR (InSAR) is a technique that compares the amplitude and phase signals received during one pass of the SAR platform over a specific geographic area with the amplitude and phase signals received during a second pass of the platform over the same area but at a different time. InSAR techniques, using satellite-based SAR platform data, can be used to produce land surface deformation products with sub cm-scale vertical resolution.

InSAR Program

ADWR has been using InSAR since 2002 to determine the spatial extent, deformation rates, and time-series history of more than thirty land subsidence features within the Phoenix, Pinal and Tucson Active Management Areas (AMAs), and several groundwater basins outside Active Management Areas in Maricopa, La Paz, Cochise, Graham, Yuma, and Navajo Counties; all covering an area greater than 4,300 square miles.

ADWR has utilized InSAR data from the following satellites:

• ERS-1
• ERS-2
• Radarsat-1
• Envisat
• ALOS-1
• ALOS-2
• TerraSAR-X
• Radarsat-2
• Sentinel-1
• NISAR

ADWR has developed an application using SAR data and InSAR processing techniques to perform long-term monitoring of land subsidence within Arizona for the purpose of improved water resource management. ADWR publishes maps of land subsidence every year. 

ADWR InSAR Program Fact Sheet

The Geophysics/Surveying Unit uses various models of survey-grade GNSS (Global Navigation Satellite System) receivers and associated equipment to perform three primary types of GNSS surveys to determine the horizontal and vertical position of discreet points: Static surveys, Real Time Kinematic (RTK) surveys and Post Processed Kinematic (PPK) surveys.

The static survey method requires long occupation times (2 or more hours, but usually at least 4-hours). The static survey method is the most accurate GNSS survey technique available today. The level of accuracy achieved in the final results is based on a number of factors (e.g. equipment type, occupation time, baseline distance, satellite availability and constellation geometry, and physical receiver environment). We primarily use the static survey method when performing our land subsidence measurements and process the data using primarily the OPUS-S and OPUS-Projects tool from the National Geodetic Survey.

The Real Time Kinematic (RTK) Survey style requires very short (seconds to minutes) occupation times and no post-processing of the GNSS data. However, this method requires that a base station (GNSS receiver occupying a location with known coordinates) or CORS (Continuously Operating Reference Station) is operating and broadcasting a correction signal that can be received by the GNSS rover receiver. The RTK survey style is used to measure a large number of survey points, in a relatively small geographic area, in a short period of time. There is a decrease in the accuracy of the final result when compared to the static survey style, but these measurements are not normally used for land subsidence monitoring.

The Post Processed Kinematic (PPK) Survey style requires an occupation time of at least thirty seconds. This method is similar to the RTK Survey style but it does not use the broadcasting correction signal. It uses the static survey data from the base station or CORS to post-process the initial point survey data.

The Geophysics/Surveying Unit uses micro-gravimeters to perform gravity surveys. The gravimeters used are a fully automated relative micro-gravity meter with a reading resolution of 0.001 mgal (milligals). They are lightweight, portable and easy to use.

Unlike absolute gravity meters, which directly measure the acceleration of gravity, relative meters measure only gravity differences between stations. Relative gravity meters are used because they are easier and faster to use in a fieldwork setting than absolute gravity meters.

The relative gravity measurements are used in conjunction with absolute gravity measurements. Gravity values are obtained at unknown stations by first measuring a station where the absolute gravity value is known, and then measuring the unknown point. This is called a gravity ‘tie.’

The micro-gravity data is used for several types of projects at ADWR: change-in-aquifer storage monitoring, depth-to-bedrock modeling studies, and aquifer parameters such as specific yield values.

Land subsidence maps and land subsidence rate maps are published each year and can be accessed at the Land Subsidence Webpage or at the Hydrology Publications Webpage

Other reports such as Land Subsidence Monitoring Reports, Hydrology Open File Reports, and Water Level Change Map Series Reports can be accessed at the Hydrology Publications Webpage

Groundwater data can be viewed online using the GWSI Database and Wells Registry Database Interactive Maps.

If you wish to request data from the Geophysics/Surveying Unit, please complete a Public Record Request