Contents lists available at ScienceDirect Geothermics journal homepage: www.elsevier.com/locate/geothermics Improved environmental monitoring of surface geothermal features through comparisons of thermal infrared, satellite remote sensing and terrestrial calorimetry Anya Seward a, ⁎ , Salman Ashraf b , Robert Reeves a , Chris Bromley a a GNS Wairakei Research centre, Private bag 2000, Taupo, 3352, New Zealand b GNS Avalon, P.O. Box 30-368, Lower Hutt, 5040, New Zealand, New Zealand ARTICLE INFO Keywords: Surface heat-loss Thermal infrared Remote sensing Calorimetry Satellite Karapiti New Zealand ABSTRACT Assessing changes in surface heat-loss at geothermally active areas provides insight into the geothermal re- servoirs at depth. Surface temperatures and heat output of steam-heated ground can be inferred through pro- cessing of thermal infrared images, as well as by direct measurements using terrestrial calorimetry. In February 2014, a high resolution aerial thermal infrared (TIR) survey and a terrestrial heat-loss survey (excluding fu- marole discharge) were carried out over Karapiti (ca. 0.35 Km 2 in the Wairakei-Tauhara Geothermal System) in the Taupo Volcanic Zone, New Zealand. Estimates of heat-loss are compared to those calculated from TIR data collected by the Landsat-8 satellite of the area. This paper discusses the processing techniques for the datasets and compares inferred surface heat losses. The aerial TIR and terrestrial measurements are in reasonable agreement with calculated surface heat-loss values for Karapiti range from 41 MW (theoretical radiation heat loss using aerial TIR) to 58 MW (total heat loss based on an empirical correlation with boiling-point depths). Satellite images show a large variation between day-time and night-time TIR assessments. The assessment of nocturnal (non-solar), radiation heat-loss is an order of magnitude lower than the total heat-loss determined from the other techniques and approximately 1/3 of the inferred radiated component calculated from the aerial TIR data. This is likely to be a consequence of diffuse, advecting-steam heat-loss, combined with an image resolution issue: the pixel resolution of the satellite image (30 × 30 m) is much larger than the typical size of the active geothermal surface manifestations (< 10 m 2 ). Because the radiated heat-loss is a non-linear function of land surface temperature, the in-pixel averaging under-estimates the radiated heat-loss. These and other pro- blems currently restrict the usefulness of repeat low-resolution satellite imagery for monitoring of surface heat- loss changes in steam-heated ground. 1. Introduction The discharge of geothermal vapour from underground reservoirs can result in areas of highly-heated and diffusely-steaming ground at the surface. The amount of heat discharged can be indicative of the relative size and recharge characteristics of the underlying geothermal resource (Hochstein and Bromley, 2005). Accurate quantification and monitoring of surface heat-loss in geothermal areas is difficult to achieve, but is important for protecting the resource and its sur- rounding environment. Such data is also important as an input for re- servoir simulation modelling and for improved sustainable manage- ment of geothermal fluid utilisation (e.g. Newson and O’Sullivan, 2004). Improvements in monitoring tools and techniques are becoming in- creasingly important in an environmentally conscientious society. Advancements in capabilities, such as remote sensing, provide many benefits to monitoring and assessing geothermal environments. They reduce costs of land-based surveys, and meet increased safety con- siderations for accessing geothermal areas. This paper compares heat- loss estimations from terrestrial measurements, aerial thermal infrared (TIR) images and satellite thermal imagery (TIRS) collected during 2014–2016, over the geothermal area at Karapiti, New Zealand. The terms heat-loss and heat flux are used often throughout the text, with heat flux referring to a measured surface heat output at a point (W m -2 ), and heat-loss referring to the surface heat output over a to- talled area (W). The Karapiti thermal area (also known as “Craters of the Moon”) is located within the Wairakei-Tauhara Geothermal System, in the Taupo Volcanic Zone (TVZ), New Zealand (Fig. 1). It encompasses https://doi.org/10.1016/j.geothermics.2018.01.007 Received 26 July 2017; Received in revised form 10 December 2017; Accepted 10 January 2018 ⁎ Corresponding author. E-mail address: a.seward@gns.cri.nz (A. Seward). Geothermics 73 (2018) 60–73 Available online 03 February 2018 0375-6505/ © 2018 Elsevier Ltd. All rights reserved. T